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[openpgp] Intent to deprecate: Insecure primitives

2015-03-13 20:23:01
First, the fait accompli:

1. Yahoo and Google have both already deprecated and removed support
for the following packet type specified for use with OpenPGPv4:

    Tag 9 (symmetrically encrypted) packets

These packets provide unauthenticated encryption and -- if supported
-- can be used in a downgrade attack on senders who only use SEIPD
packets. See
for details.

2. Yahoo and GnuPG have both already deprecated V3 public keys for any
use. We recommend that other implementations do the same.


Second, the near future:

Yahoo has deprecated, and intends to disable support for all uses, of
the following primitives and packet types specified for use with
OpenPGP v4:

- Symmetric cipher algorithms: IDEA, TDES, CAST5, Blowfish, Twofish
- Asymmetric algorithms, generally: RSA-ES, DSA.
- Asymmetric algorithms, unless > 3070 bit key length: RSA-S, RSA-E, ELG-E.
- Compression algorithms: ZLIB. (It provides no benefits over DEFLATE,
and is more malleable.)
- Hash algorithms: MD5, SHA-1, RIPEMD160, SHA-2-224.

We do not, at present, support any of the CAMELLIA algorithms or
BZIP2. It is unlikely that we will do so in future.

At present, we anticipate removing support for these primitives no
later than May 1, 2015.


Third, other things that will be deprecated soonish:

1. Inconsistent combinations of primitives. In particular, it is
likely that we will not support RFC 6637 keys or packets unless they
conform to the 128-bit or 192-bit subprofiles specified in that
document. (We do not at present support P-521, but if we add support
for that, we would support an analogous "256-bit" subprofile.)

2. AES-128. The efficiency of multi-target attacks leaves no safety
margin for cryptanalysis. The performance difference between AES-128
and AES-256 on typical messages is negligible.


Finally, other things that may eventually result in messages or keys
being treated as invalid:

1. A published public key that is more than 1 year old. (This is
mainly taken care of by requiring > 3070 bit RSA keys...)
2. Signature by a public key which has ever signed a message or key
using MD-5 or SHA-1.
3. A compressed or literal data packet tag that is unusually formatted.
4. A compression method other than "Uncompressed".

David Leon Gil
Senior Paranoid

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