[v6] Determine signature hash prefs based on recipient keys instead of signing key #1802
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twiss
reviewed
Oct 30, 2024
…lgo when signing In `openpgp.sign`, the signing key preferences are considered instead, since no "recipient keys" are available. The hash algo selection logic has been reworked as follows: if `config.preferredHashAlgo` appears in the prefs of all recipients, we pick it; otherwise, we use the strongest supported algo (note: SHA256 is always implicitly supported by all keys), as long as it is compatible with the signing key (e.g. ECC keys require minimum digest sizes). Previously, only the preferences of the signing key were used to determine the hash algo to use, but this is in contrast to the RFC: https://www.rfc-editor.org/rfc/rfc9580.html#section-5.2.3.16-2 . Also, an algo stronger than `config.preferredHashAlgo` would be used, if the signing key declared it as first preference. With this change, `config.preferredHashAlgo` is picked even if it's weaker than the preferences of the recipient keys.
If given, the signature will be generated using the preferred hash algo from the recipient keys. Otherwise, the signing key preferences are used (this was also the existing behavior). Note: when signing through `openpgp.encrypt`, the `encryptionKeys` are automatically used as recipient keys.
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twiss
approved these changes
Oct 30, 2024
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Changes:
The signature will be generated using the preferred hash algo from the recipient keys:
openpgp.encrypt, when passingsigningKeys, theencryptionKeysare treated as recipient keysopenpgp.sign, arecipientKeysoption has been addedIf no recipient keys are available, the signing key preferences are used (this was also the existing behavior).
The hash algo selection logic has been reworked as follows:
if
config.preferredHashAlgoappears in the prefs of all recipients, we pick it;otherwise, we use the strongest supported algo (note: SHA256 is always implicitly supported by all keys), as long as it is compatible with the signing key (e.g. ECC keys require minimum digest sizes).
With this change,
config.preferredHashAlgois picked even if it's weaker than the preferences of the recipient keys.Previously, only the preferences of the signing key were used to determine the hash algo to use, but this is in contrast to the RFC: https://www.rfc-editor.org/rfc/rfc9580.html#section-5.2.3.16-2 .
Also, an algo stronger than
config.preferredHashAlgowould be used, if the signing key declared it as first preference.