Prevent length extension attack on network seed #9
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As described in urbit/urbit-key-generation#55, the use of SHA2-256 in networking seed derivation is vulnerable to length-extension attacks. This change patches that vulnerability. Since network seeds have already been generated with revision 0, that case needs to remain backwards-compatible, and thus will not change. All other cases will change, doing SHA2-256d (hashing twice with SHA2-256) to protect against length extension attacks. Note that network seeds generated with revision 0 are not vulnerable to length extension attacks themselves, because the revision number as part of the salt should never have leading zeroes.
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Thanks for handling this, Fang. LGTM |
Fang-
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Nov 23, 2018
For details on these changes, see urbit/fora-posts#9.
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As described in urbit/urbit-key-generation#55, the use of SHA2-256 in networking seed derivation is vulnerable to length-extension attacks. This change patches that vulnerability.
Since network seeds have already been generated with revision 0, that case needs to remain backwards-compatible, and thus will not change. All other cases will change, doing SHA2-256d (hashing twice with SHA2-256) to protect against length extension attacks.
Note that network seeds generated with revision 0 are not vulnerable to length extension attacks themselves, because the revision number as part of the salt should never have unnecessary leading zeroes.