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