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9. Constants This section describes the constants used in OpenPGP. Note that these tables are not exhaustive lists; an implementation MAY implement an algorithm not on these lists. See the section "Notes on Algorithms" below for more discussion of the algorithms. 9.1. Public Key Algorithms ID Algorithm -- --------- 1 - RSA (Encrypt or Sign) 2 - RSA Encrypt-Only 3 - RSA Sign-Only 16 - Elgamal (Encrypt-Only), see [ELGAMAL] 17 - DSA (Digital Signature Standard) 18 - Reserved for Elliptic Curve 19 - Reserved for ECDSA 20 - Elgamal (Encrypt or Sign) 21 - Reserved for Diffie-Hellman (X9.42, as defined for IETF-S/MIME) 100 to 110 - Private/Experimental algorithm. Implementations MUST implement DSA for signatures, and Elgamal for encryption. Implementations SHOULD implement RSA keys. Implementations MAY implement any other algorithm. 9.2. Symmetric Key Algorithms ID Algorithm -- --------- 0 - Plaintext or unencrypted data 1 - IDEA [IDEA] 2 - Triple-DES (DES-EDE, as per spec - 168 bit key derived from 192) 3 - CAST5 (128 bit key, as per RFC 2144) 4 - Blowfish (128 bit key, 16 rounds) [BLOWFISH] 5 - SAFER-SK128 (13 rounds) [SAFER] 6 - Reserved for DES/SK 7 - Reserved for AES with 128-bit key 8 - Reserved for AES with 192-bit key 9 - Reserved for AES with 256-bit key[WG: 10 - Twofish with 256-bit key]. 100 to 110 - Private/Experimental algorithm. Implementations MUST implement Triple-DES. Implementations SHOULD implement IDEA and CAST5.Implementations MAY implement any other algorithm. 9.3. Compression Algorithms ID Algorithm -- --------- 0 - Uncompressed 1 - ZIP (RFC 1951) 2 - ZLIB (RFC 1950) 100 to 110 - Private/Experimental algorithm. Implementations MUST implement uncompressed data. Implementations SHOULD implement ZIP. Implementations MAY implement ZLIB. 9.4. Hash Algorithms ID Algorithm Text Name -- --------- ---- ---- 1 - MD5 "MD5" 2 - SHA-1 "SHA1" 3 - RIPE-MD/160 "RIPEMD160" 4 - Reserved for double-width SHA (experimental) 5 - MD2 "MD2" 6 - Reserved for TIGER/192 "TIGER192" 7 - Reserved for HAVAL (5 pass, 160-bit) "HAVAL-5-160" 100 to 110 - Private/Experimental algorithm. Implementations MUST implement SHA-1. Implementations SHOULD implement MD5.

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Updated: 1999-09-30 wkoch