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IPsec

In computing, Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in virtual private networks (VPNs).

IPsec includes protocols for establishing mutual authentication between agents at the beginning of a session and negotiation of cryptographic keys to use during the session. IPsec can protect data flows between a pair of hosts (host-to-host), between a pair of security gateways (network-to-network), or between a security gateway and a host (network-to-host). IPsec uses cryptographic security services to protect communications over Internet Protocol (IP) networks. It supports network-level peer authentication, data origin authentication, data integrity, data confidentiality (encryption), and protection from replay attacks.

History
Starting in the early 1970s, the Advanced Research Projects Agency sponsored a series of experimental ARPANET encryption devices, at first for native ARPANET packet encryption and subsequently for TCP/IP packet encryption; some of these were certified and fielded. From 1986 to 1991, the NSA sponsored the development of security protocols for the Internet under its Secure Data Network Systems (SDNS) program. This brought together various vendors including Motorola who produced a network encryption device in 1988. The work was openly published from about 1988 by NIST and, of these, Security Protocol at Layer 3 (SP3) would eventually morph into the ISO standard Network Layer Security Protocol (NLSP).

In 1992, the US Naval Research Laboratory (NRL) was funded by DARPA CSTO to implement IPv6 and to research and implement IP encryption in 4.4 BSD, supporting both SPARC and x86 CPU architectures. DARPA made its implementation freely available via MIT. Under NRL's DARPA-funded research effort, NRL developed the IETF standards-track specifications (RFC 1825 through RFC 1827) for IPsec. NRL's IPsec implementation was described in their paper in the 1996 USENIX Conference Proceedings. NRL's open-source IPsec implementation was made available online by MIT and became the basis for most initial commercial implementations.

The Internet Engineering Task Force (IETF) formed the IP Security Working Group in 1992 to standardize openly specified security extensions to IP, called IPsec. The NRL developed standards were published by the IETF as RFC-1825 through RFC-1827.

Security architecture
The initial IPv4 suite was developed with few security provisions. As a part of the IPv4 enhancement, IPsec is a layer 3 OSI model or internet layer end-to-end security scheme. In contrast, while some other Internet security systems in widespread use operate above the network layer, such as Transport Layer Security (TLS) that operates above the transport layer and Secure Shell (SSH) that operates at the application layer, IPsec can automatically secure applications at the internet layer.

IPsec is an open standard as a part of the IPv4 suite and uses the following protocols to perform various functions:

 * Authentication Header (AH) provides connectionless data integrity and data origin authentication for IP datagrams and provides protection against IP header modification attacks and replay attacks.
 * Encapsulating Security Payload (ESP) provides confidentiality, connectionless data integrity, data origin authentication, an anti-replay service (a form of partial sequence integrity), and limited traffic-flow confidentiality.
 * Internet Security Association and Key Management Protocol (ISAKMP) provides a framework for authentication and key exchange, with actual authenticated keying material provided either by manual configuration with pre-shared keys, Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys (KINK), or IPSECKEY DNS records.   The purpose is to generate the security associations (SA) with the bundle of algorithms and parameters necessary for AH and/or ESP operations.

Authentication Header
The Security Authentication Header (AH) was developed at the US Naval Research Laboratory in the early 1990s and is derived in part from previous IETF standards' work for authentication of the Simple Network Management Protocol (SNMP) version 2. Authentication Header (AH) is a member of the IPsec protocol suite. AH ensures connectionless integrity by using a hash function and a secret shared key in the AH algorithm. AH also guarantees the data origin by authenticating IP packets. Optionally a sequence number can protect the IPsec packet's contents against replay attacks, using the sliding window technique and discarding old packets.

AH operates directly on top of IP, using IP protocol number 51.
 * In IPv4, AH prevents option-insertion attacks. In IPv6, AH protects both against header insertion attacks and option insertion attacks.
 * In IPv4, the AH protects the IP payload and all header fields of an IP datagram except for mutable fields (i.e. those that might be altered in transit), and also IP options such as the IP Security Option (RFC 1108). Mutable (and therefore unauthenticated) IPv4 header fields are DSCP/ToS, ECN, Flags, Fragment Offset, TTL and Header Checksum.
 * In IPv6, the AH protects most of the IPv6 base header, AH itself, non-mutable extension headers after the AH, and the IP payload. Protection for the IPv6 header excludes the mutable fields: DSCP, ECN, Flow Label, and Hop Limit.

The following AH packet diagram shows how an AH packet is constructed and interpreted:
 * Next Header (8 bits) : Type of the next header, indicating what upper-layer protocol was protected. The value is taken from the list of IP protocol numbers.
 * Payload Len (8 bits) : The length of this Authentication Header in 4-octet units, minus 2. For example, an AH value of 4 equals 3×(32-bit fixed-length AH fields) + 3×(32-bit ICV fields) − 2 and thus an AH value of 4 means 24 octets. Although the size is measured in 4-octet units, the length of this header needs to be a multiple of 8 octets if carried in an IPv6 packet. This restriction does not apply to an Authentication Header carried in an IPv4 packet.
 * Reserved (16 bits) : Reserved for future use (all zeroes until then).
 * Security Parameters Index (32 bits) : Arbitrary value which is used (together with the destination IP address) to identify the security association of the receiving party.
 * Sequence Number (32 bits) : A monotonic strictly increasing sequence number (incremented by 1 for every packet sent) to prevent replay attacks. When replay detection is enabled, sequence numbers are never reused, because a new security association must be renegotiated before an attempt to increment the sequence number beyond its maximum value.
 * Integrity Check Value (multiple of 32 bits) : Variable length check value. It may contain padding to align the field to an 8-octet boundary for IPv6, or a 4-octet boundary for IPv4.

Encapsulating Security Payload
The IP Encapsulating Security Payload (ESP) was developed at the Naval Research Laboratory starting in 1992 as part of a DARPA-sponsored research project, and was openly published by IETF SIPP Working Group drafted in December 1993 as a security extension for SIPP. This ESP was originally derived from the US Department of Defense SP3D protocol, rather than being derived from the ISO Network-Layer Security Protocol (NLSP). The SP3D protocol specification was published by NIST in the late 1980s, but designed by the Secure Data Network System project of the US Department of Defense. Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. It provides origin authenticity through source authentication, data integrity through hash functions and confidentiality through encryption protection for IP packets. ESP also supports encryption-only and authentication-only configurations, but using encryption without authentication is strongly discouraged because it is insecure.

Unlike Authentication Header (AH), ESP in transport mode does not provide integrity and authentication for the entire IP packet. However, in tunnel mode, where the entire original IP packet is encapsulated with a new packet header added, ESP protection is afforded to the whole inner IP packet (including the inner header) while the outer header (including any outer IPv4 options or IPv6 extension headers) remains unprotected.

ESP operates directly on top of IP, using IP protocol number 50.

The following ESP packet diagram shows how an ESP packet is constructed and interpreted:
 * Security Parameters Index (32 bits) : Arbitrary value used (together with the destination IP address) to identify the security association of the receiving party.
 * Sequence Number (32 bits) : A monotonically increasing sequence number (incremented by 1 for every packet sent) to protect against replay attacks. There is a separate counter kept for every security association.
 * Payload data (variable) : The protected contents of the original IP packet, including any data used to protect the contents (e.g. an Initialisation Vector for the cryptographic algorithm). The type of content that was protected is indicated by the Next Header field.
 * Padding (0-255 octets) : Padding for encryption, to extend the payload data to a size that fits the encryption's cipher block size, and to align the next field.
 * Pad Length (8 bits) : Size of the padding (in octets).
 * Next Header (8 bits) : Type of the next header. The value is taken from the list of IP protocol numbers.
 * Integrity Check Value (multiple of 32 bits) : Variable length check value. It may contain padding to align the field to an 8-octet boundary for IPv6, or a 4-octet boundary for IPv4.

Security association
The IPsec protocols use a security association, where the communicating parties establish shared security attributes such as algorithms and keys. As such, IPsec provides a range of options once it has been determined whether AH or ESP is used. Before exchanging data, the two hosts agree on which symmetric encryption algorithm is used to encrypt the IP packet, for example AES or ChaCha20, and which hash function is used to ensure the integrity of the data, such as BLAKE2 or SHA256. These parameters are agreed for the particular session, for which a lifetime must be agreed and a session key.

The algorithm for authentication is also agreed before the data transfer takes place and IPsec supports a range of methods. Authentication is possible through pre-shared key, where a symmetric key is already in the possession of both hosts, and the hosts send each other hashes of the shared key to prove that they are in possession of the same key. IPsec also supports public key encryption, where each host has a public and a private key, they exchange their public keys and each host sends the other a nonce encrypted with the other host's public key. Alternatively if both hosts hold a public key certificate from a certificate authority, this can be used for IPsec authentication.

The security associations of IPsec are established using the Internet Security Association and Key Management Protocol (ISAKMP). ISAKMP is implemented by manual configuration with pre-shared secrets, Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys (KINK), and the use of IPSECKEY DNS records. RFC 5386 defines Better-Than-Nothing Security (BTNS) as an unauthenticated mode of IPsec using an extended IKE protocol. C. Meadows, C. Cremers, and others have used formal methods to identify various anomalies which exist in IKEv1 and also in IKEv2.

In order to decide what protection is to be provided for an outgoing packet, IPsec uses the Security Parameter Index (SPI), an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identifies a security association for that packet. A similar procedure is performed for an incoming packet, where IPsec gathers decryption and verification keys from the security association database.

For IP multicast a security association is provided for the group, and is duplicated across all authorized receivers of the group. There may be more than one security association for a group, using different SPIs, thereby allowing multiple levels and sets of security within a group. Indeed, each sender can have multiple security associations, allowing authentication, since a receiver can only know that someone knowing the keys sent the data. Note that the relevant standard does not describe how the association is chosen and duplicated across the group; it is assumed that a responsible party will have made the choice.

Keepalives
To ensure that the connection between two endpoints has not been interrupted, endpoints exchange keepalive messages at regular intervals, which can also be used to automatically reestablish a tunnel lost due to connection interruption.

Dead Peer Detection (DPD) is a method of detecting a dead Internet Key Exchange (IKE) peer. The method uses IPsec traffic patterns to minimize the number of messages required to confirm the availability of a peer. DPD is used to reclaim the lost resources in case a peer is found dead and it is also used to perform IKE peer failover.

UDP keepalive is an alternative to DPD.

Modes of operation
The IPsec protocols AH and ESP can be implemented in a host-to-host transport mode, as well as in a network tunneling mode.

Transport mode
In transport mode, only the payload of the IP packet is usually encrypted or authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when the authentication header is used, the IP addresses cannot be modified by network address translation, as this always invalidates the hash value. The transport and application layers are always secured by a hash, so they cannot be modified in any way, for example by translating the port numbers.

A means to encapsulate IPsec messages for NAT traversal {NAT-T} has been defined by RFC documents describing the NAT-T mechanism.

Tunnel mode
In tunnel mode, the entire IP packet is encrypted and authenticated. It is then encapsulated into a new IP packet with a new IP header. Tunnel mode is used to create virtual private networks for network-to-network communications (e.g. between routers to link sites), host-to-network communications (e.g. remote user access) and host-to-host communications (e.g. private chat).

Tunnel mode supports NAT traversal.

Symmetric encryption algorithms
Cryptographic algorithms defined for use with IPsec include:
 * HMAC-SHA1/SHA2 for integrity protection and authenticity.
 * TripleDES-CBC for confidentiality
 * AES-CBC and AES-CTR for confidentiality.
 * AES-GCM and ChaCha20-Poly1305 providing confidentiality and authentication together efficiently.

Refer to RFC 8221 for details.

Key exchange algorithms

 * Diffie–Hellman (RFC 3526)
 * ECDH (RFC 4753)

Authentication algorithms

 * RSA
 * ECDSA (RFC 4754)
 * PSK (RFC 6617)
 * EdDSA (RFC 8420)

Implementations
The IPsec can be implemented in the IP stack of an operating system. This method of implementation is done for hosts and security gateways. Various IPsec capable IP stacks are available from companies, such as HP or IBM. An alternative is so called bump-in-the-stack (BITS) implementation, where the operating system source code does not have to be modified. Here IPsec is installed between the IP stack and the network drivers. This way operating systems can be retrofitted with IPsec. This method of implementation is also used for both hosts and gateways. However, when retrofitting IPsec the encapsulation of IP packets may cause problems for the automatic path MTU discovery, where the maximum transmission unit (MTU) size on the network path between two IP hosts is established. If a host or gateway has a separate cryptoprocessor, which is common in the military and can also be found in commercial systems, a so-called bump-in-the-wire (BITW) implementation of IPsec is possible.

When IPsec is implemented in the kernel, the key management and ISAKMP/IKE negotiation is carried out from user space. The NRL-developed and openly specified "PF_KEY Key Management API, Version 2" is often used to enable the application-space key management application to update the IPsec security associations stored within the kernel-space IPsec implementation. Existing IPsec implementations usually include ESP, AH, and IKE version 2. Existing IPsec implementations on Unix-like operating systems, for example, Solaris or Linux, usually include PF_KEY version 2.

Embedded IPsec can be used to ensure the secure communication among applications running over constrained resource systems with a small overhead.

Standards status
IPsec was developed in conjunction with IPv6 and was originally required to be supported by all standards-compliant implementations of IPv6 before RFC 6434 made it only a recommendation. IPsec is also optional for IPv4 implementations. IPsec is most commonly used to secure IPv4 traffic.

IPsec protocols were originally defined in RFC 1825 through RFC 1829, which were published in 1995. In 1998, these documents were superseded by RFC 2401 and RFC 2412 with a few incompatible engineering details, although they were conceptually identical. In addition, a mutual authentication and key exchange protocol Internet Key Exchange (IKE) was defined to create and manage security associations. In December 2005, new standards were defined in RFC 4301 and RFC 4309 which are largely a superset of the previous editions with a second version of the Internet Key Exchange standard IKEv2. These third-generation documents standardized the abbreviation of IPsec to uppercase “IP” and lowercase “sec”. “ESP” generally refers to RFC 4303, which is the most recent version of the specification.

Since mid-2008, an IPsec Maintenance and Extensions (ipsecme) working group is active at the IETF.

Alleged NSA interference
In 2013, as part of Snowden leaks, it was revealed that the US National Security Agency had been actively working to "Insert vulnerabilities into commercial encryption systems, IT systems, networks, and endpoint communications devices used by targets" as part of the Bullrun program. There are allegations that IPsec was a targeted encryption system.

The OpenBSD IPsec stack came later on and also was widely copied. In a letter which OpenBSD lead developer Theo de Raadt received on 11 Dec 2010 from Gregory Perry, it is alleged that Jason Wright and others, working for the FBI, inserted "a number of backdoors and side channel key leaking mechanisms" into the OpenBSD crypto code. In the forwarded email from 2010, Theo de Raadt did not at first express an official position on the validity of the claims, apart from the implicit endorsement from forwarding the email. Jason Wright's response to the allegations: "Every urban legend is made more real by the inclusion of real names, dates, and times. Gregory Perry's email falls into this category. … I will state clearly that I did not add backdoors to the OpenBSD operating system or the OpenBSD Cryptographic Framework (OCF)." Some days later, de Raadt commented that "I believe that NETSEC was probably contracted to write backdoors as alleged. … If those were written, I don't believe they made it into our tree." This was published before the Snowden leaks.

An alternative explanation put forward by the authors of the Logjam attack suggests that the NSA compromised IPsec VPNs by undermining the Diffie-Hellman algorithm used in the key exchange. In their paper, they allege the NSA specially built a computing cluster to precompute multiplicative subgroups for specific primes and generators, such as for the second Oakley group defined in RFC 2409. As of May 2015, 90% of addressable IPsec VPNs supported the second Oakley group as part of IKE. If an organization were to precompute this group, they could derive the keys being exchanged and decrypt traffic without inserting any software backdoors.

A second alternative explanation that was put forward was that the Equation Group used zero-day exploits against several manufacturers' VPN equipment which were validated by Kaspersky Lab as being tied to the Equation Group and validated by those manufacturers as being real exploits, some of which were zero-day exploits at the time of their exposure. The Cisco PIX and ASA firewalls had vulnerabilities that were used for wiretapping by the NSA.

Furthermore, IPsec VPNs using "Aggressive Mode" settings send a hash of the PSK in the clear. This can be and apparently is targeted by the NSA using offline dictionary attacks.

Standards track

 * : The ESP DES-CBC Transform
 * : The Use of HMAC-MD5-96 within ESP and AH
 * : The Use of HMAC-SHA-1-96 within ESP and AH
 * : The ESP DES-CBC Cipher Algorithm With Explicit IV
 * : The NULL Encryption Algorithm and Its Use With IPsec
 * : The ESP CBC-Mode Cipher Algorithms
 * : The Use of HMAC-RIPEMD-160-96 within ESP and AH
 * : More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE)
 * : The AES-CBC Cipher Algorithm and Its Use with IPsec
 * : Using Advanced Encryption Standard (AES) Counter Mode With IPsec Encapsulating Security Payload (ESP)
 * : Negotiation of NAT-Traversal in the IKE
 * : UDP Encapsulation of IPsec ESP Packets
 * : The Use of Galois/Counter Mode (GCM) in IPsec Encapsulating Security Payload (ESP)
 * : Security Architecture for the Internet Protocol
 * : IP Authentication Header
 * : IP Encapsulating Security Payload
 * : Extended Sequence Number (ESN) Addendum to IPsec Domain of Interpretation (DOI) for Internet Security Association and Key Management Protocol (ISAKMP)
 * : Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (IKEv2)
 * : Cryptographic Suites for IPsec
 * : Using Advanced Encryption Standard (AES) CCM mode with IPsec Encapsulating Security Payload (ESP)
 * : The Use of Galois Message Authentication Code (GMAC) in IPsec ESP and AH
 * : IKEv2 Mobility and Multihoming Protocol (MOBIKE)
 * : Online Certificate Status Protocol (OCSP) Extensions to IKEv2
 * : Using HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512 with IPsec
 * : The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX
 * : Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
 * : Using Authenticated Encryption Algorithms with the Encrypted Payload of the Internet Key Exchange version 2 (IKEv2) Protocol
 * : Better-Than-Nothing Security: An Unauthenticated Mode of IPsec
 * : Modes of Operation for Camellia for Use with IPsec
 * : Redirect Mechanism for the Internet Key Exchange Protocol Version 2 (IKEv2)
 * : Internet Key Exchange Protocol Version 2 (IKEv2) Session Resumption
 * : IKEv2 Extensions to Support Robust Header Compression over IPsec
 * : IPsec Extensions to Support Robust Header Compression over IPsec
 * : Internet Key Exchange Protocol Version 2 (IKEv2)
 * : Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)
 * : Internet Key Exchange Protocol Version 2 (IKEv2) Message Fragmentation
 * : Signature Authentication in the Internet Key Exchange Version 2 (IKEv2)
 * : ChaCha20, Poly1305, and Their Use in the Internet Key Exchange Protocol (IKE) and IPsec

Experimental RFCs

 * : Repeated Authentication in Internet Key Exchange (IKEv2) Protocol

Informational RFCs

 * : PF_KEY Interface
 * : The OAKLEY Key Determination Protocol
 * : A Traffic-Based Method of Detecting Dead Internet Key Exchange (IKE) Peers
 * : IPsec-Network Address Translation (NAT) Compatibility Requirements
 * : Design of the IKEv2 Mobility and Multihoming (MOBIKE) Protocol
 * : Requirements for an IPsec Certificate Management Profile
 * : Problem and Applicability Statement for Better-Than-Nothing Security (BTNS)
 * : Integration of Robust Header Compression over IPsec Security Associations
 * : Using Advanced Encryption Standard Counter Mode (AES-CTR) with the Internet Key Exchange version 02 (IKEv2) Protocol
 * : IPsec Cluster Problem Statement
 * : IPsec and IKE Document Roadmap
 * : Suite B Cryptographic Suites for IPsec
 * : Suite B Profile for Internet Protocol Security (IPsec)
 * : Secure Password Framework for Internet Key Exchange Version 2 (IKEv2)

Best current practice RFCs

 * : Guidelines for Specifying the Use of IPsec Version 2

Obsolete/historic RFCs

 * : Security Architecture for the Internet Protocol (obsoleted by RFC 2401)
 * : IP Authentication Header (obsoleted by RFC 2402)
 * : IP Encapsulating Security Payload (ESP) (obsoleted by RFC 2406)
 * : IP Authentication using Keyed MD5 (historic)
 * : Security Architecture for the Internet Protocol (IPsec overview) (obsoleted by RFC 4301)
 * : IP Encapsulating Security Payload (ESP) (obsoleted by RFC 4303 and RFC 4305)
 * : The Internet IP Security Domain of Interpretation for ISAKMP (obsoleted by RFC 4306)
 * : The Internet Key Exchange (obsoleted by RFC 4306)
 * : Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (obsoleted by RFC 4835)
 * : Internet Key Exchange (IKEv2) Protocol (obsoleted by RFC 5996)
 * : IKEv2 Clarifications and Implementation Guidelines (obsoleted by RFC 7296)
 * : Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH) (obsoleted by RFC 7321)
 * : Internet Key Exchange Protocol Version 2 (IKEv2) (obsoleted by RFC 7296)

title: IPsec


text:
User:Marco Maggesi

See: http://www.math.unifi.it/~maggesi/

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: User:Marco Maggesi


text:
Telluride, Colorado

Telluride is the county seat and most populous town of San Miguel County in the southwestern portion of the U.S. state of Colorado. The town is a former silver mining camp on the San Miguel River in the western San Juan Mountains. The first gold mining claim was made in the mountains above Telluride in 1875, and early settlement of what is now Telluride followed. The town was founded in 1878.

Telluride sits in a box canyon. Steep forested mountains and cliffs surround it, with Bridal Veil Falls situated at the canyon's head. Numerous weathered ruins of old mining operations dot the hillsides. A free gondola connects the town with its companion town, Mountain Village, at the base of the ski area. Telluride and the surrounding area have featured prominently in popular culture, and it is the subject of several popular songs. It is especially known for its ski resort and slopes during the winter, as well as an extensive festival schedule during the summer, including the Hot Air Balloon Festival, which traditionally occurs the first weekend in June.

The Telluride Historic District, which includes a significant portion of the town, is listed on the National Register of Historic Places and is also one of Colorado's 20 National Historic Landmarks. The town population was 2,607 in the 2020 United States Census.

Mining days
Gold was first discovered in Colorado near present-day Denver, setting off the Pike's Peak gold rush of 1858. The Smuggler gold vein above Telluride, and placer gold in the San Miguel River, were discovered in 1875. John Fallon made the first claim in Marshal Basin above Telluride in 1875 and early settlement of Telluride followed. The town was founded in 1878. Telluride was originally named "Columbia", but due to confusion with Columbia, California, the name was changed by the post office. The town was named after valuable ore compounds of the chemical element tellurium, a metalloid element which forms natural tellurides, the most notable of which are telluride ores of gold and silver. Although gold telluride minerals were never actually found in the mountains near Telluride, the area's mines were rich in zinc, lead, copper, silver, and ores which contained gold in other forms.

Telluride began slowly because of its isolated location. In 1881, a toll road was opened by Otto Mears, which allowed wagons to go where only pack mules could go before. This increased the number of people in Telluride, but it was still expensive to get gold-rich ore out of the valley.

In June 1889, Butch Cassidy, before becoming associated with his gang, the "Wild Bunch", robbed the San Miguel Valley Bank in Telluride. This was his first major recorded crime. He exited the bank with $24,580 and later became famous as a bank robber.

In 1891, the Rio Grande Southern Railroad, also begun by Mears, arrived in Telluride, eventually building a two-stall engine house, water facilities, a section house and a bunkhouse, sidings, and a depot. It continued further up the valley to end its Telluride branch at Pandora, serving the mines and the town until 1952. The cheaper and consistent transportation for passengers and freight allowed miners and goods to flow into the San Miguel town and ore to flow out to the mills and foundries elsewhere. This brought a brief but unprecedented boom to Telluride before the Panic of 1893.

Around the turn of the 20th century, there were serious labor disputes in the mines near Telluride. The Colorado National Guard was called out and there were deaths on both sides. Unions were formed as miners joined the Western Federation of Miners in 1896. 1899 brought big changes as union strike action led most mines to grant miners $3 a day for an 8-hour day's work plus a boarding pay of $1 a day. At this time, workers were putting in 10- to 12-hour days and the mines ran 24 hours a day. Work conditions were treacherous, with mines above 12000 ft, a lack of safety measures, and bitter weather in winter months. Even the boarding houses were precariously placed on the mountainsides.

Telluride's labor unrest occurred against the backdrop of a statewide struggle between miners and mine owners. Bulkeley Wells was one mine operator considerably hostile to the union. The Telluride Miners' Union was led by Vincent St. John. The disappearance of mine guard William J. Barney, which Wells declared a "murder", created much intrigue and national interest. The accusations, animosity, gunplay, and expulsions that followed were part of an ongoing struggle throughout Colorado's mining communities which came to be called the Colorado Labor Wars.

In 1891, Telluride's L. L. Nunn joined forces with George Westinghouse to build the Ames Hydroelectric Generating Plant, an alternating current power station, near Telluride. The plant supplied power to the Gold King Mine 3.5 mi away. This was the first successful demonstration of long-distance transmission of industrial-grade alternating current power and used two 100 hp Westinghouse alternators, one working as a generator producing 3,000 volts, 133 Hertz, single-phase AC, and the other used as an AC motor. This hydroelectric AC power plant predated the Westinghouse plant at Niagara Falls by four years. Nunn and his brother Paul built power plants in Colorado, Utah, Idaho, Montana, Mexico, and the Ontario Power plant at Niagara Falls on the Canadian side. Nunn developed a keen interest in education as part of his electrical power companies, and in conjunction with Cornell University built the Telluride House at Cornell in 1909 to educate promising students in electrical engineering. Later, Nunn along with Charles Walcott, started the non-profit Telluride Association. Nunn founded Deep Springs College in 1917. Each year, the Telluride Tech Festival honors Nunn, inventor Nikola Tesla, and Westinghouse, along with current-day technology and science leaders.

Telluride's most famous historic mines are the Tomboy, Pandora, Smuggler-Union, Nellie, and Sheridan mines. Beginning in 1939, the hard-rock mining operations in the Red Mountain and Telluride mining districts began a lengthy consolidation under the Idarado Mining Company (Idarado), now a division of Newmont Mining. The consolidation ended in 1953 with Idarado's acquisition of the Telluride Mines. Idarado kept the underground workings and mill operations open at Telluride's Pandora hard-rock mine until 1978. When the mine officially closed, the snow which tormented Telluride's miners became the town's new source of income, in the form of skiing and tourism. The documentary video "the YX factor" chronicles the transition from mining to skiing and the influx of "hippies" in the late 1960s and early 1970s in the words of local residents and commentators such as Peter Yarrow and Tom Hayden.

Skiing era
Mining was Telluride's only industry until 1972 when the first ski lift was installed by Telluride Ski Resort founder Joseph T. Zoline and his Telluride Ski Corporation (Telco). Zoline bought the land for the future resort in 1969 and began to craft the slopes. Along with his mountain manager, Telluride native Bill "Sr." Mahoney, they slowly and thoughtfully put together a plan for the sustained development of Telluride and the region. As mining phased out and a new service industry phased in, the local population changed sharply. Mining families fled Telluride to settle in places like Moab, Utah, where uranium mining offered hope of continued employment. Mining families were replaced by what locals referred to as "hippies", young people with a 1960s worldview that often clashed with the values of Telluride's old-timers. These newcomers were characterized as idle "trust funders" drawn to the town for a casual lifestyle and outdoor excitements such as hang gliding, mountain climbing, and kayaking.

The new population opposed town growth and economic expansion, including growth due to tourism and skiing. At one point, a serious effort was made to ban cars from the city limits and force visitors to use horse-drawn carts. The 1970s had fluctuating snowfalls and economic recession, but the town's music and film festivals flourished. They exposed hundreds of thousands to the grandeur of the valley for the first time and created iconic associations with elite entertainers. Meanwhile, ski area founder Joe Zoline worked to develop one of the best mountains in North America for expert skiers, and created the infrastructure for tourism that respected Telluride's need to stay small.

As the final ore carts were rolling out of the Pandora mine, tourists began to discover Telluride's views, skiing, and autumn color changes. After the brutal snow drought of 1976 nearly wiped out the embryonic ski and lodging industry, the town started to rebound economically. In 1978, Ron Allred and his partner Jim Wells bought a stake in the ski area to form the Telluride Company. They expanded the infrastructure by adding a gondola connecting Telluride with the Mountain Village.

The Grateful Dead played Telluride on August 16 and 17, 1987, riding the recent success of In the Dark.

During the 1980s, Telluride developed a reputation as "Colorado's best-kept secret", which paradoxically made it one of the better-known resort communities. Wealthy skiers flocked to the mountain all winter, and sightseers kept hotel rooms full all summer. Telluride also became notorious in the drug counterculture as a drop point for Mexican smugglers and a favorite place for wealthy importers to enjoy downtime. The town was even featured in the hit song by Glenn Frey from Miami Vice, "Smugglers Blues". Telluride was living up to its Wild West history. This type of attention helped differentiate it from Aspen. The festivals and Telluride's bad-boy image attracted celebrities like Tom Cruise, Oprah Winfrey, and Oliver Stone. By the mid-1990s, Telluride had shed both its mining personality and drug image to establish itself as a premier resort town balancing modern culture with fascinating western history. In 2003, Prospect Bowl, an extension to the ski area opened, providing the resort with many new trails and runs. In 2007–08, the ski area opened some of the most extreme, inbound, hike-to terrain in the country. Most lifts in the area are high-speed quad chairs capable of holding four passengers. The highest lift on the mountain reaches 12570 ft.

Telluride has a free box that is well supported by the community.

Geography
Telluride has an elevation of 8750 ft in an isolated spot in Southwest Colorado. From the west, Colorado Route 145 is the most common way into Telluride; two other passes enter the town, Imogene Pass and Black Bear Pass.

On the eastern side of town, there are two waterfalls: Ingram Falls, which is visible from town, and Bridal Veil Falls and the Bridal Veil Hydroelectric plant, which are just out of sight from town to the right of Ingram. The power plant house was leased for some time by Eric Jacobson, who restored the house and the generator inside. The hydroelectric plant was built in 1895 to power the Smuggler-Union Mine.

The town is served by air transportation via Telluride Regional Airport (TEX), once the highest elevation commercial airport in the United States at 9,070 feet. The airport is considered challenging by pilots because of frequent adverse weather conditions, high elevation, and the extremely rugged mountain terrain surrounding the airport on nearly all sides. Major airline service is provided seasonally into Montrose (MTJ), approximately 70 mi north by road.

Climate
Telluride has a humid continental climate (Dfb). The coldest month is January, averaging 18.2 F, and the hottest July, which averages 58.7 F. Precipitation peaks as snow in winter and as thunderstorms in summer with a dry period in late spring. Telluride gets moderate precipitation all year due to its altitude, averaging 20.37 in of water equivalent precipitation, including 130.8 in inches of snow, each year.

Demographics
As of the census of 2000, there were 2,221 people, 1,013 households, and 357 families residing in the town. The population density was 3,143.3 /mi2. There were 1,938 housing units at an average density of 2,742.8 /mi2. The racial makeup of the town was 92.57% White, 0.81% Native American, 0.72% Asian, 0.41% African American, 4.14% from other races, and 1.35% from two or more races. Hispanic or Latino of any race were 7.20% of the population.

There were 1,013 households, out of which 19.1% had children under the age of 18 living with them, 25.2% were married couples living together, 6.1% had a female householder with no husband present, and 64.7% were non-families. 31.9% of all households were made up of individuals, and 1.6% had someone living alone who was 65 years of age or older. The average household size was 2.19 and the average family size was 2.79.

In the town, the population was spread out, with 14.3% under the age of 18, 12.2% from 18 to 24, 50.9% from 25 to 44, 20.8% from 45 to 64, and 1.9% who were 65 years of age or older. The median age was 31 years. For every 100 females, there were 122.8 males. For every 100 females aged 18 and over, there were 127.4 males.

The median income for a household in the town was $51,938, and the median income for a family was $66,136. Males had a median income of $35,329 versus $30,096 for females. The per capita income for the town was $38,832. About 8.5% of families and 11.5% of the population were below the poverty line, including 16.2% of those under age 18 and 6.9% of those aged 65 or over.

Tourism
Beyond the ski lifts, Telluride is now widely recognized as an all-season resort. Telluride Ski Resort is the main attraction in the winter. But when summer comes around, Telluride transforms into an outdoor recreation hot spot, with tourists visiting to enjoy mountain biking, hiking, river rafting, sightseeing, and more. The Telluride Tourism Board promotes tourism in the region.

Telluride features over 30 hiking trails ranging in difficulty level. Some of the hiking routes include Ajax Peak, Bear Creek Falls, Hope Lake, and Bridal Veil Falls. Hiking season begins in May and lasts until early October, with waterfalls gushing in June and wildflowers at their peak in early July. The trails range from quick and easy runs to multi-day hiking trips that reach an elevation of 14000 ft. Nearly all the trails feature waterfalls, wildflowers, and high alpine lakes.

Telluride is also home to many endurance events. The Imogene Pass Run from Ouray to Telluride, the Hardrock 100, held in July, has a major aid station in the town park. The Fall Tilt, a 12-hour downhill mountain biking event, is held in Mountain Village each September. And the 40 mi Telluride Mountain Run loops the town in a wide swath that includes some of the most difficult and scenic trails in the area.

Transportation
Telluride is served by Telluride Regional Airport. Scheduled flight options are limited, due to the airport's somewhat short runway and frequent closures under bad weather, so most passengers going to Telluride use Montrose Regional Airport, 67 mi to the north.

Free public transportation is provided in Telluride. The bus system, called Galloping Goose, makes a complete loop around the town. A gondola lift links Telluride with Mountain Village.

Telluride's free gondola is the only one of its kind in North America. It stops at three stations, namely Telluride, San Sophia, and Mountain Village, and was the first leg of a transportation agreement for the Telluride Region that was stipulated as part of the Mountain Village zoning expansion that would provide free gondola service from the Town of Telluride and the Mountain Village to the Aldasoro Development, the West Meadows Development, the Valley Floor Development, and the West Meadows Development to virtually eliminate the use or need for a car in the Telluride Region of San Miguel County. It is a 13-minute ride and reaches an elevation of 10540 ft at the San Sophia station.

Regional bus service is provided by the San Miguel Authority for Regional Transportation (SMART).

Telluride is part of Colorado's Bustang intercity bus service network. It is on the Durango-Grand Junction Outrider line.
 * Major highways
 * Colorado 145.svg State Highway 145 is part of the San Juan Skyway. It connects Telluride to Cortez and Naturita. This road also gives access to State Highway 62, the main route to Denver, Montrose and other important places in Colorado.

There are two alternate passes to enter the town, namely Imogene Pass and Black Bear Pass. Both require high clearance or four-wheel-drive vehicles.
 * Mountain passes

In popular culture
Clive Cussler's 1998 novel Atlantis Found is partially set in Telluride. The novel features signs of an ancient civilization being found in an underground chamber next to a mine outside the city.

In Justin Cronin's 2010 novel The Passage, Telluride is the site of a secret military compound used to test a purported "longevity drug" on death row inmates.

The production of The Hateful Eight directed by Quentin Tarantino began filming near Telluride in January 2015.

The Coen brothers 2018 film The Ballad of Buster Scruggs used Telluride as a filming location for the vignette "All Gold Canyon", based on a short story by Jack London.

The Kia Telluride vehicle is named after the town.

title: Telluride, Colorado


text:
Talk:Vi (text editor)

traceable to Bill Joy?
The explanation given in the editor's comment was unclear. Offhand, the source went to AT&T with Horton, and the AT&T source ultimately (through many developers) became what's on AIX, HP-UX and Solaris (though the last provides vim in the most recent releases). TEDickey (talk) 22:17, 24 June 2020 (UTC)

 * Maybe Nvi is a good example here? The source code can not be attributed/traced to Bill Joy because the point of Nvi was avoiding license issues.
 * On the other hand the phrasing "Some current implementations of vi..." complicates things because for Nvi might be an implementation of the 'Concept'/specification of Vi but not of the original Vi editor. Moikvin (talk) 20:16, 15 January 2022 (UTC)

edit not supported by reliable sources
There's no reliable sources for vi written by "Mary Horton" (aside from some primary sources which aren't usable here) TEDickey (talk) 23:50, 4 July 2020 (UTC)

 * Is your concern that Mark / Mary Ann Horton didn't work on vi, or that Mary Ann Horton isn't the same person as Mark Horton? Both of these seem to be supported by https://www.usenix.org/system/files/login/articles/spring20_09_horton.pdf.  Dan Bloch (talk) 00:58, 5 July 2020 (UTC)

 * The source you're citing is written long after the events occurred, and isn't really relevant to the ~40-year-old sources which document the work. There's nothing that I could use, at any rate TEDickey (talk) 01:30, 5 July 2020 (UTC)

 * The question isn't what source was cited, it's what sources exist. New reliable sources consistently refer to her as Mary Ann Horton, even when describing her work done under an earlier name.  This is exactly what WP:NAMECHANGES asks us to consider.  You can't cherry-pick to say this is the only article about her work on vi, therefore we can ignore how she's referred to in newer sources describing all the rest of her work in that same period.  Msnicki (talk) 13:25, 5 July 2020 (UTC)

 * https://en.wikipedia.org/wiki/Wikipedia:Gender_identity Irrelevant. Wikipedia style, as well as basic respect for trans people, dictates otherwise. Her name is, as a point of fact, Mary Horton. — Preceding unsigned comment added by 75.166.197.195 (talk) 01:40, 5 July 2020 (UTC)
 * I agree. WP:Gender identity strongly supports using Ms. Horton's preferred name. It states, ''"When a subject changes names as part of coming out as transgender, it is often impossible to continue to use that person's former name without misgendering them and thus causing harm as discussed in #Self-identification and #Transphobia.'"  Msnicki (talk) 13:10, 5 July 2020 (UTC)

 * I support treating Ms. Horton with basic human respect and referring to her by her preferred name. To do otherwise seems unnecessarily rude.  Msnicki (talk) 01:58, 5 July 2020 (UTC)

 * However, it's debatable whether that follows the guideline in WP:NAMECHANGES. For this topic, almost all sources (except for the previously mentioned primary sources), use the older name.  By the way, your comments about rude are off-topic, there's no need to insert promotional comments. TEDickey (talk) 09:34, 5 July 2020 (UTC)

 * My point is that it's disrespectful and mean-spirited to refer to a transperson by their old name. When people do that, it's often motivated by animus.  Whether that was the motivation in this case is irrelevant; this is what the behavior communicates and we shouldn't do it.  Moreover, I find the guidelines you cite to support using her current name.  Exactly one source is cited that was written before the name change.  But new sources, e.g., in The Daily Beast, clearly refer to Ms. Horton by her current name.  From WP:NAMECHANGES, "If the reliable sources written after the change is announced routinely use the new name, Wikipedia should follow suit and change relevant titles to match."  This should not be a hard choice.  We should be respectful and refer to her by her preferred name.  Msnicki (talk) 12:20, 5 July 2020 (UTC)

 * Wikipedia's policy on this is "Use context to determine which name or names to provide on a case-by-case basis", which doesn't help much but is a reminder that there's no general agreement. (WP:NAMECHANGES is only about article titles. WP:Gender identity is an essay and not policy.)  Manual of Style/Gender identity, which is also not policy but which is a draft policy and could some day become policy, suggests something like "Mary Ann Horton, then known as Mark Horton".  Could everyone live with that? Dan Bloch (talk) 14:27, 5 July 2020 (UTC)
 * No. This is only an incidental mention of Ms. Horton.  We're reporting her contribution and that's all that's important.  There is no reason to call attention to completely irrelevant personal details of her name and gender change years later in an article about vi.  This has nothing to do with vi.  We have a WP:BLP about her titled Mary Ann Horton that explains things for anyone who's confused in the first seven words.  For me, the name chosen as the title of the WP:BLP pretty much settles the matter of whether we should use an individual's current or former name to refer to them here and elsewhere on Wikipedia.  If you disagree with that choice, I think the BLP talk page is the place to take your argument, not here.  Msnicki (talk) 14:51, 5 July 2020 (UTC)

 * At this point there's general agreement that Ms. Horton be identified as such. The issue is whether also mentioning the name used in the sources of the time is of value to readers. Dan Bloch (talk) 16:37, 6 July 2020 (UTC)
 * There is no value to that. Most people are aware that people change their names for a variety of reasons and can follow the hyperlink if they are curious to know more about Ms. Horton's reason.  The source being cited is what it is as a reliable source for the claim being made.  Msnicki (talk) 18:16, 6 July 2020 (UTC)

 * I used terms like [Latin for [transcription of numeral 6 is] six] in other programs [app naming / code commments], eg when you are looking for namings like this, you might be not that unreasonable [I am a loser, but I thought that maybe long term, well, ye know] [multilingual wiktionary?] — Preceding unsigned comment added by 2A0A:A540:BE8:0:ACC6:17F2:88CC:E35A (talk) 23:19, 18 May 2022 (UTC)

Requested move 1 December 2023

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: moved. (closed by non-admin page mover) NmWTfs85lXusaybq (talk) 04:05, 8 December 2023 (UTC)

Vi → Vi (text editor) – (and redirect Vi to VI) Even with the second letter lowercase, this is a simple two-letter combination for which there is no primary topic. This subject's long-term significance not at the same height as primary topics Ra, Ur, qi, or pi. Google Search's first results are for the text editor, but this may be inauthentic – Google also jokingly displays Did you mean: EMACS. A Google Scholar search for "vi" -author:vi shows results almost entirely for "vi" as the Roman numeral (capitalized of course). Lastly, this topic doesn't significantly clear Vi (League of Legends) in terms of |Vi_(League_of_Legends) pageviews. Hameltion (talk | contribs) 17:30, 1 December 2023 (UTC)

 * Yes!(but*): I buy it. (To me), (almost always), "VI" and "vi" are just annoying things to write instead of [6 (number)]. Where that is not the case, (in context), "VI" and ".vi" are US or British [Virgin Islands]; v.i. is [verb intransitive]; "Vi" is Vi [Violet (given name)]; and yes "vi" can be [vi (text editor)], but only because I have (rarely) read of it. (Btw, I never heard of vi, and can't recall having heard it spoken.) I think someone looking up "vi", "VI", "Vi", "V.I.", or "v.i." probably is not looking for "6", and is less likely to be looking for [vi (text editor)] than for one of the others. So yes, move [Vi] to [Vi (text editor)], *WITH REDIRECT (so that the existing 7 redirects to [Vi] get automatically corrected). AFTER the corrections happen, you could change [Vi] to redirect to [VI] (the existing disambiguation page), -OR- move [VI] to [Vi] (is there a norm? A quick look finds CA, CI, DU, EM, FM, IL, LB, MD, NC, ND, NY, PC, PR, and WA; but Bo, Do, Nm, Oe, Or, Oz, and Pa. (NJ, Nj, NZ, and Nz redirect to articles.) -A876 (talk) 21:15, 1 December 2023 (UTC)

 * Comment Without a way to differentiate on the lower-case first letter, it's probably true that there's no primary topic for vi/Vi, though an argument could be made on the basis of long-term significance. However, it's also true that the text editor is by far the most common destination from VI. Wikinav shows it having twice the outgoing pageviews of Vodaphone Idea and four times the outgoing pageviews of Vi (League of Legends). And this in spite of lower-case vi also having its own page. If vi is merged into the DAB, the DAB should lead off with a "VI most commonly refers to:" section a la Mercury. I'm happy to add this section, but if there are any objections now is the time to raise them, not later. Dan Bloch (talk) 18:54, 2 December 2023 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
 * Support there are uses that get many more more views[] like British Virgin Islands	with 37,909 and Vi (League of Legends) has 8,342 compared with 16,124 for this one.  Crouch, Swale  ( talk ) 18:29, 3 December 2023 (UTC)
 * Support per nom. -- Necrothesp (talk) 14:33, 5 December 2023 (UTC)

Vi Modes
"...including allowing the cursor keys to work in input mode" could be referring to Insert mode, as mentioned earlier in the article under "Interface". I haven't heard Insert mode referred to as Input mode before in any documentation or articles about Vi, so I'm skeptical as to its usage here. Also, pressing Escape while in Insert mode does not enter Command mode as the article suggests; commands are entered by prefixing them with a colon. Finally, there is a third mode that isn't mentioned at all, Replace mode, which is entered by pressing capital R while in Normal mode. TechPersonYT (talk) 23:39, 16 April 2024 (UTC)

Rivalry with Emacs
Is is worth mentioning the Editor War? Quoting that article, “the rivalry [between users of the Emacs and vi] has become an enduring part of hacker culture and the free software community.” --2001:16B8:ABA2:6E00:10F6:5BAB:6090:730A (talk) 11:41, 27 April 2024 (UTC)

title: Talk:Vi (text editor)