Implement RSA verification #4952
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Managed to navigate through RFC 8017 and mostly looks good.
| unchecked { | ||
| // cache and check length | ||
| uint256 length = mod.length; | ||
| if (length < 0x40 || length != sig.length) { |
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I guess we reject length less than 0x40 because it wouldn't be secure. I wonder if 0x40 was arbitrarily chosen. If so, we need to evaluate it carefully, as far as I remember, RSA's security is p * q so a 512 bits signature is crackable in reasonable time.
Found this as a reference, but seems like 512 bits (0x40 bytes) signatures are pretty much broken.
https://github.com/tomrittervg/cloud-and-control/blob/master/gnfs-info/factoring-howto.txt
RFC 3447 is from 2003 and was superseded by RFC 8017, though, I couldn't find a recommendation for the mod length. Allegedly, 512 bits security was first broken in 1999, so my estimations say that we might increase this to 0x80 at least.
Needs discussion
| if (_unsafeReadBytes1(buffer, length - 50) == 0x31) { | ||
| // case: sha256Explicit | ||
| offset = 0x34; | ||
| params = 0x003031300d060960864801650304020105000420000000000000000000000000; | ||
| mask = 0xffffffffffffffffffffffffffffffffffffffff000000000000000000000000; | ||
| } else if (_unsafeReadBytes1(buffer, length - 48) == 0x2F) { | ||
| // case: sha256Implicit | ||
| offset = 0x32; | ||
| params = 0x00302f300b060960864801650304020104200000000000000000000000000000; | ||
| mask = 0xffffffffffffffffffffffffffffffffffff0000000000000000000000000000; | ||
| } else { | ||
| // unknown | ||
| return false; | ||
| } |
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From the RFC, Section 9.2 defines the algorithm identifier, but turns out the explicit NULL param is mentioned in Appendix C.
Allowed EMSA-PKCS1-v1_5 digest algorithms.PKCS1-v1-5DigestAlgorithms ALGORITHM-IDENTIFIER ::= {
{ OID id-md2 PARAMETERS NULL }|
{ OID id-md5 PARAMETERS NULL }|
{ OID id-sha1 PARAMETERS NULL }|
{ OID id-sha224 PARAMETERS NULL }|
{ OID id-sha256 PARAMETERS NULL }|
{ OID id-sha384 PARAMETERS NULL }|
{ OID id-sha512 PARAMETERS NULL }|
{ OID id-sha512-224 PARAMETERS NULL }|
{ OID id-sha512-256 PARAMETERS NULL }
}When id-md2 and id-md5 are used in an AlgorithmIdentifier, the parameters field shall have a value of type NULL. When id-sha1, id-sha224, id-sha256, id-sha384, id-sha512, id-sha512-224, and id-sha512-256 are used in an AlgorithmIdentifier, the parameters (which are optional) SHOULD be omitted, but if present, they SHALL have a value of type NULL. However, implementations MUST accept AlgorithmIdentifier values both without parameters and with NULL parameters.
Pending to verify it, but then the byte difference between 0x31 and 0x2F should come from the explicit null param (that is 05 00). I'm just not sure how to encode that section explicitly,
Work in progress. Based on https://github.com/adria0/SolRsaVerify
Tests:
SigVer15_186-3.rspfrom here and automatically run all test examples.For now, only sha256 is supported.
@nobles/hashprovides all the function we need to generate the digest, andSigVer15_186-3.rspcontains more tests.Do we want to support more?
PR Checklist
npx changeset add)