I’m going to attempt to collect open-source implementations of SHA-1 here. There are many more of them than MD5, which is appropriate, considering that SHA-1 is the most widely used message digest function to date.
Obligatory Wikipedia page on SHA-1.
FIPS PUB 180-4: Secure Hash Standard, March 2012, covers SHA-1 and SHA-2. In this document, all but SHA-1 are variants of SHA-2 – e.g. SHA-256 and SHA-512 are 256-bit and 512-bit output variants of SHA-2, respectively.
NIST 800-107: Recommendations for Applications Using Approved Hash Algorithms is also worth reading.
NIST has a list of all validated SHA-1 implementations: SHS Validation List. As of 2/22/2013, there are 2024 of them, although to be fair, a lot of the entries are incremental updates by folks like IBM/Tivoli, and the majority of entries are in the past few years (I suppose this means increased scrutiny on security and trust).
1995, FIPS 180-1
FIPS 180-1 – Secure Hash Standard. This was the formal release of the SHA-1 algorithm. FIPS 180-1 was superceded by FIPS 180-2, FIPS 180-3 and now FIPS 180-4. The document had pseudo-code and several test vectors. While MD5 has a single author, Ronald Rivest, SHA-1 was invented by the NSA.
2001, RFC 3174 (Donald Eastlake and Paul Jones)
RFC 3174 has an implementation of SHA-1 in C by Donald Eastlake and Paul E. Jones. The date on the RFC is 2001, but it’s likely that drafts and code were written several years before this.
1998, Packetizer (Paul Jones)
There is a slight variant from Paul E. Jones, linked in Secure Hashing Algorithm (SHA-1),which appears to have been written around 1998, with an update in 2009. There are a handful of changes from the code in RFC 3174. I don’t know if this is the same Paul E. Jones from RFC 3174.
2006, RFC 4634 (Donald Eastlake and Paul Jones)
RFC 4634 is an update to handle input of arbitrary bit length. RFC and presumably code written by Donald Eastlake and Paul Jones, 2006.
2011, RFC 6234 (Donald Eastlake and Tony Hansen)
RFC 6234 replaces RFC 4634, and adding HMAC and HKDF functionality. The RFC (and presumably code) was written by Donald Eastlake and Tony Hansen, 2011.
1998, Ghostscript (Steve Reid, James Brown)
SHA-1 in C from ghostscript.
There are validated implementations of SHA-1 in the OpenSSL FIPS Object Model, at http://www.openssl.org/source/.
IBM Crypto for C (ICC) is listed as “a non-proprietary FIPS 140-2 cryptographic module”. I couldn’t find source available, though, so I’ll probably remove this.
Mozilla Network Security Services (NSS) contains SHA-1 implementations.
Crypto++ (Wei Dai)
Crypto++ has SHA-1 implementations
2001, Botan (Jack Lloyd)
Botan has SHA-1 implementations.
2004, Aaron Gifford
Secure Hash Algorithm (SHA) has BSD licensed code for SHA-1.
2006, Cryptlib (Peter Gutman)
Cryptlib has SHA-1.
2009, Git (Linus Torvalds)
Commit d7c208a9, Add new optimized C ‘block-sha1′ routines, introduced an optimized version of the Mozilla SHA1 function to git, reportedly about 30% faster. This version would not work on some architectures, because it requires an architecture that allows unaligned 32-bit loads.
Also see comments on mailing lists, including Re: x86 SHA1: Faster than OpenSSL for development history.
This is in coreutils, which is GPLv3, but a message from Linus indicated he might be willing to stick with the MPL license, since he started from mozilla-sha1; see thread Linus’ sha1 is much faster! There’s also a separate implementation from George Spelvin in a thread spun off from that thread.
2011, smallsha1 (Micael Hildenborg)
smallsha1 is written in C++. It uses an old-style BSD license, the one with an advertising clause, so it’s probably not suitable for use by most companies.
2012, Nayuki Minasi
Fast SHA-1 hash implementation in x86 assembly
Source code available, but not open source. Gets about 327 MiB/sec on a Core 2 Q6600 2.4 GHz, compared with (claimed) OpenSSL speed of 305 MiB/sec on equivalent hardware.