On 4/11/2018 1:36 AM, James Bottomley wrote: > On Tue, 2018-04-10 at 23:01 +0100, Martin Townsend wrote: >> Using openssl to get the signature in my x509 cert >> >> Signature Algorithm: sha256WithRSAEncryption >> 68:82:cc:5d:f9:ee:fb:1a:77:72:a6:a9:c6:4c:cc:d7:f6:2a: >> 17:a5:db:bf:5a:2b:8d:39:60:dc:a0:93:39:45:0f:bc:a7:e8: >> 7f:6c:06:84:2d:f3:c1:94:0a:60:56:1c:50:78:dc:34:d1:87: >> >> So there's an extra 0x00 and the signature is 257 bytes so I guess >> this is upsetting CAAM, just need to work out where it's coming from, >> or whether it's valid and CAAM should be handling it. > > A signature is just a bignum so leading zeros are permitted because > it's the same numeric value; however, there are normalization > procedures that require stripping the leading zeros, say before doing a > hash or other operation which would be affected by them. > > CAAM should definitely handle it on the "be liberal in what you accept" > principle. The kernel should probably remove the leading zeros on the > "be conservative in what you do" part of the same principle. > Looking at the generic SW implementation (crypto/rsa.c, rsa_verify()), leading zeros are removed: s = mpi_read_raw_from_sgl(req->src, req->src_len); CAAM implementation of rsa is not doing this (though it is removing leading zeros when reading public, private keys). It has to be fixed. Thanks for the report. >> I notice that in my stack trace I have pkcs1pad_verify which >> suggests some sort of padding? > > Yes, RSA has various forms of padding because the information being > encrypted is usually much smaller than the encryption unit; PKCS1 is > the most common (although its now deprecated in favour of OAEP because > of all the padding oracle problems). > RSA padding has been intentionally added as a template, wrapping "textbook" (raw) RSA primitives. For PKCS#1 v1.5, a template instantiation is called pkcs1pad(rsa, hash_alg). Currently in kernel the only supported RSA padding scheme is PKCS#1 v1.5. When implemented, another scheme - for e.g. OAEP - would be added in a similar way, as a template: oaep(rsa, ...). Horia
