Test PGPSignatures with LegacyEd25519 keys with short MPIs #1706
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vanitasvitae
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Jun 12, 2024
| @@ -455,7 +455,7 @@ else if (getKeyAlgorithm() == PublicKeyAlgorithmTags.EDDSA_LEGACY) | |||
| { | |||
| byte[] a = BigIntegers.asUnsignedByteArray(sigValues[0].getValue()); | |||
| byte[] b = BigIntegers.asUnsignedByteArray(sigValues[1].getValue()); | |||
| if (a.length + b.length == Ed25519.SIGNATURE_SIZE) | |||
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Here, a.length or b.length could be 31 instead of the the expected 32.
Since Ed25519 signatures are shorter than Ed448 signatures, the new comparison should hold.
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The test vector (see as PGP packet here) demonstrates the issue by having a short 31-octet |
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Fix is already part of main, so I reduced the PR to only contain the test. |
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#1706 Test PGPSignatures with LegacyEd25519 keys with short MPIs See merge request root/bc-java!31
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In main as c51be49 |
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With legacy ed25519 we need to detect the curve (curve25519 / curve448) based on the length of the encoding (see #1675, most notably 105dbef).
However, I noticed, that some ed25519 signatures MPIs are shorter than the expected 2*32 octets (leading 0s), resulting in the code misinterpreting the signature as an ed448 signature. This in turn causes signature verification failures for good signatures.
This patch catches this edge case by allowing short MPIs.