Overhaul ECDSA signature parsing: strict DER, compact sigs, tests, lower-S #334
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sipa
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Added a commit that introduces a snippet for lax DER parsing (tested!). |
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Addressed many comments. |
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Added a certainly_not_der as output from the BER generator, and tests using it. |
This commit adds functions: * secp256k1_rand_bits, which works like secp256k1_rand32, but consumes less randomness * secp256k1_rand_int, which produces a uniform integer over any range * secp256k1_rand_bytes_test, which works like secp256k1_rand256_test but for arbitrary byte array
Update the unit tests to make use of the new RNG functions.
There are now 2 encoding formats supported: 64-byte "compact" and DER. The latter is strict: the data has to be exact DER, though the values inside don't need to be valid.
This shows a snippet of code to do lax DER parsing, without obeying to any particular standard.
ECDSA signature verification now requires normalized signatures (with S in the lower half of the range). In case the input cannot be guaranteed to provide this, a new function secp256k1_ecdsa_signature_normalize is provided to preprocess it.
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ACK |
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Oct 22, 2015
0c6ab2f Introduce explicit lower-S normalization (Pieter Wuille) fea19e7 Add contrib/lax_der_parsing.h (Pieter Wuille) 3bb9c44 Rewrite ECDSA signature parsing code (Pieter Wuille) fa57f1b Use secp256k1_rand_int and secp256k1_rand_bits more (Pieter Wuille) 49b3749 Add new tests for the extra testrand functions (Pieter Wuille) f684d7d Faster secp256k1_rand_int implementation (Pieter Wuille) 251b1a6 Improve testrand: add extra random functions (Pieter Wuille)
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There are now 2 encoding formats supported: 64-byte "compact" and DER. The latter is strict: the data has to be exact DER, though the values inside don't need to be valid.
This means that applications that need more than strict DER as input, it needs to have a parser itself. I wish there was a better solution, but there really isn't. Any subset of BER to implement would be arbitrary, incompatible with many other applications anyway, or be very complex and nearly untestable. Despite that, a code snippet to do so (with extensive testing) is included in the contrib/ directory now.
Finally, by default, we now require non-malleable signatures (by requiring the lower-S form), but a separate function is provided to normalize a signature before verification if needed.