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diff --git a/doc/OpenPGP b/doc/OpenPGP new file mode 100644 index 0000000..794f669 --- /dev/null +++ b/doc/OpenPGP @@ -0,0 +1,116 @@ + GnuPG and OpenPGP + ================= + + See RFC-4880 for a description of OpenPGP. These notes are older + than RFC-4880 and refer to the predecessor of the specs (RFC-2440). + + + Compatibility Notes + =================== + GnuPG (>=1.0.3) is in compliance with RFC2440 despite these exceptions: + + * With GnuPG >= 2.1.0 all support for version 3 keys has been + removed. Thus there is no more compatibility with PGP-2. Users + who need to be able to decrypt old PGP 2 messages should use + GnuPG 1.4.x along with the option --allow-weak-digest-algos. + + * With GnuPG >= 2.1.0 all signatures (on messages and keys) are + created using version 4 signatures. Support for verifying + version 3 signature is still available. + + * (9.2) states that IDEA SHOULD be implemented. This is not done + due to patent problems. + UPDATE: Since version 1.4.13 (or GnuPG 2.x with Libgcrypt 1.6) + IDEA support has been added to allow decryption of old + PGP-2 encrypted material. + + All MAY features are implemented with this exception: + + * multi-part armored messages are not supported. + MIME (rfc2015) should be used instead. + + Most of the OPTIONAL stuff is implemented. + + There are a couple of options which can be used to override some + RFC requirements. This is always mentioned with the description + of that options. + + A special format of partial packet length exists for v3 packets + which can be considered to be in compliance with RFC1991; this + format is only created if a special option is active. + UPDATE: This support has been removed with version 1.3.6. + + GnuPG uses a S2K mode of 101 for GNU extensions to the secret key + protection algorithms. This number is not defined in OpenPGP, but + given that this number is in a range which is used at many other + places in OpenPGP for private/experimental algorithm identifiers, + this should be not a too bad choice. The 3 bytes "GNU" are used to + identify this as a GNU extension - see the file DETAILS for a + definition of the used data formats. + + + Some Notes on OpenPGP / PGP Compatibility: + ========================================== + + * PGP 5.x does not accept V4 signatures for anything other than + key material. The GnuPG option --force-v3-sigs mimics this + behavior. + + * PGP 5.x does not recognize the "five-octet" lengths in + new-format headers or in signature subpacket lengths. + + * PGP 5.0 rejects an encrypted session key if the keylength + differs from the S2K symmetric algorithm. This is a bug in its + validation function. + + * PGP 5.0 does not handle multiple one-pass signature headers and + trailers. Signing one will compress the one-pass signed literal + and prefix a V3 signature instead of doing a nested one-pass + signature. + + * When exporting a private key, PGP 2.x generates the header + "BEGIN PGP SECRET KEY BLOCK" instead of "BEGIN PGP PRIVATE KEY + BLOCK". All previous versions ignore the implied data type, and + look directly at the packet data type. + + * In a clear-signed signature, PGP 5.0 will figure out the correct + hash algorithm if there is no "Hash:" header, but it will reject + a mismatch between the header and the actual algorithm used. The + "standard" (i.e. Zimmermann/Finney/et al.) version of PGP 2.x + rejects the "Hash:" header and assumes MD5. There are a number + of enhanced variants of PGP 2.6.x that have been modified for + SHA-1 signatures. + + * PGP 5.0 can read an RSA key in V4 format, but can only recognize + it with a V3 keyid, and can properly use only a V3 format RSA + key. + + * Neither PGP 5.x nor PGP 6.0 recognize ElGamal Encrypt and Sign + keys. They only handle ElGamal Encrypt-only keys. + + + Parts of this document are taken from: + ====================================== + + OpenPGP Message Format + draft-ietf-openpgp-formats-07.txt + + + Copyright 1998 by The Internet Society. All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph + are included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. |