Crypto++  
   Free C++ library for cryptography: includes ciphers, message authentication codes, one-way hash functions, public-key cryptosystems, and key agreement schemes.
   http://www.eskimo.com/~weidai/cryptlib.html

OpenSSL  
   A collaborative effort to develop a robust, commercial-grade, full-featured, and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) protocols as well as a full-strength general purpose cryptography
   http://www.openssl.org/

Emacs Cryptographic Library and Tools  
   Includes code for IDEA, Blowfish, SHA-1, MD5, RC16 (RC4 extension), an initial implementation of DES and a few related toys.
   http://web.mit.edu/thouis/www/ecrypto.html

BSAFEeay  
   A free, public domain implementation of RSA Data Security's BSAFE API, using the SSLeay crypto library.
   https://www.cypherpunks.to/bsafeeay/

CTC  
   CTClib (PGP-interoperable ANSI C encryption software library) and CTCjava (Java crypto components and application).
   http://www.bifroest.demon.co.uk/ctc/

Catacomb Cryptographic Library  
   Library of cryptographic primitives in ANSI C, including block ciphers and hash functions, together with generic modes of operation. Also includes simple key management system, multiprecision arithmetic, and public key algorithms.
   http://www.excessus.demon.co.uk/misc-hacks/index.html#catacomb

libmcrypt  
   Supports the following algorithms; BLOWFISH, TWOFISH, DES, TripleDES, 3-WAY, SAFER-sk64, SAFER-sk128, SAFER+, LOKI97, GOST, RC2, RC6, MARS, IDEA, RIJNDAEL-128 (AES), RIJNDAEL-192, RIJNDAEL-256, SERPENT, CAST-128, CAST-256, ARCFOUR and WAKE. ANSI C.
   http://mcrypt.hellug.gr/#_libmcrypt

Network Security Services  
   Mozilla's NSS, is a set of libraries designed to support cross-platform development of security-enabled server applications.
   http://mozilla.org/projects/security/pki/nss/

CypherMath - Cryptographic Math Package  
   Gives your applications access to multi-precision integer math routines with just a function call. Full source code available. For VB, C++, or embedded systems.
   http://www.cyphercalc.com/math

Applied Cryptography Code  
   The code from the Applied Cryptography disk, available outside the US.
   ftp://ftp.zedz.net/pub/crypto/applied-crypto/

BeeCrypt  
   An open source cryptography library that contains highly optimized C and assembler implementations of many well-known algorithms including Blowfish, MD5, SHA-1, Diffie-Hellman and ElGamal.
   http://www.virtualunlimited.com/products/beecrypt/

Entrust Dev-Net  
   A variety of tools to add PKI functionality to your application.
   https://www.entrust.com/developer/software/index.htm

RC-Crypt  
   Implementation of RC5 (128) in C.
   http://www.ricksoft.co.uk/downloads/rccrypt/rccrypt.htm

MD5 Homepage (unofficial)  
   Information and implementation in various languages.
   http://userpages.umbc.edu/%7emabzug1/cs/md5/md5.html

The Iraqi Block Cipher (IBC)  
   Contains C source code.
   http://the.wiretapped.net/security/cryptography/algorithms/ibc/ibc.c

RSA MD5 Visual C++  
   An implementation of the message digest algorithm. Includes a performance measurement facility.
   http://www.langfine.com/rsa_md5.htm

TPCrypt by Technology Pathways LLC  
   Cryptographic classes for Microsoft .NET. Includes DES, TripleDES, RC2, and Rijndael (AES) implementations.
   http://www.TechPathways.com/DesktopDefault.aspx?tabindex=3&tabid=3

Dragonate Technologies Ltd.  
   Offers Elliptic Curve software. including ECDSACom, an ActiveX control, and borZoi, an open source library. Includes product descriptions and contact information.
   http://www.dragongate-technologies.com/products.html

Snapcrypt - Cryptography Algorithms  
   A library for the TMS320C54x DSP, contains algorithms for symmetric block ciphers, one-way hash functions, public key encryption and digital signature.
   http://www.snapshield.com/Products_licensing_fs.html

Hidden Field Equations (HFE) in Java  
   A free implementation of the public key cryptography system with source code and documentation.
   http://www.christopher-wolf.de/hfe/

PrimeInk  
   Tools to work with X.509 certificates and revocation lists, various security syntax and messaging formats, a time stamping API, public key encryption algorithms, key exchange protocols, and a range of secure hash functions. Lists types of uses and compat
   http://www.cryptomathic.com/products/primeink_index.html

SSL++ -- C++ Wrapper arround OpenSSL library  
   SSL++ is simple C++ library encapsulating OpenSSL functionality to make it simple and easily accessible to C++ programmers.
   http://www.total-knowledge.com/progs/sslpp

The source code of the 128-bit PC1 cipher algorithm  
   In C, Delphi, Java, Perl and Visual Basic.
   http://membres.lycos.fr/pc1

Sysepub  
   A Java open source cipher that combines one time pad with public and private keys.
   http://it.geocities.com/teutoburgo/java/sysepub.html

QuartzLight in Java  
   Implements the public key signature system QuartzLight in Java where QuartzLight refers to a research version of the Quartz standard.
   http://www.christopher-wolf.de/ql/

Punkroy and the Cypher Project  
   Collection of programming examples on encryption including: file encryption, steganography in images and sound, data base record encryption, and password verification. All written in Pascal, all source code available.
   http://drque.net/Punkroy/Programs.html

SlavaSoft QuickHash Library  
   Add hash (MD2, MD5, SHA-1, SHA-2, RIPEMD-160, PANAMA, TIGER), checksum (CRC32, ADLER32) and HMAC (HMAC-MD5, HMAC-SHA1, HMAC-SHA256, HMAC-SHA384, HMAC-SHA512, HMAC-RIPEMD160, HMAC-PANAMA, HMAC-TIGER) calculations to your Windows apps quickly and easily. C+
   http://www.slavasoft.com/quickhash

Botan  
   An open-source C++ crypto library that includes block and stream ciphers, hash functions, MACs, and public key algorithms, along with an easy to use filter-based interface.
   http://botan.randombit.net/

Nickellie Encryption Toolkit  
   The Nickellie Encryption Toolkit is a data and file encryption library that provides a COM interface to simplify development of Windows and Pocket PC software that requires encryption.
   http://www.nickellie.com/encryption.asp