Re: How to extract ECC signature bytes from EVP_DigestSignFinal's signature
I dug into source - it's in DER format so a sleezy hacked function is this: ( I use curve NID_X9_62_prime256v1 ) ECDSA_SIG * sig BIGNUM * r; BIGNUM * s; /* A correct DER-encoded signature has the following form: 0x30: a header byte indicating a compound structure. A 1-byte length descriptor for all what follows. 0x02: a header byte indicating an integer. A 1-byte length descriptor for the R value The R coordinate, as a big-endian integer. 0x02: a header byte indicating an integer. A 1-byte length descriptor for the S value. The S coordinate, as a big-endian integer. */ r = BN_bin2bn( src+ 4, 32, NULL ); // create new bn here s = BN_bin2bn( src+ 4 +32 + 2, 32, NULL ); if(!BN_copy(sig-r, r)) goto err; if(!BN_copy(sig-s, s)) goto err; -- View this message in context: http://openssl.6102.n7.nabble.com/How-to-extract-ECC-signature-bytes-from-EVP-DigestSignFinal-s-signature-tp48878p4.html Sent from the OpenSSL - User mailing list archive at Nabble.com. __ OpenSSL Project http://www.openssl.org User Support Mailing Listopenssl-users@openssl.org Automated List Manager majord...@openssl.org
Re: How to extract ECC signature bytes from EVP_DigestSignFinal's signature
On Tue, Mar 18, 2014, axisofevil wrote: I dug into source - it's in DER format so a sleezy hacked function is this: ( I use curve NID_X9_62_prime256v1 ) ECDSA_SIG * sig BIGNUM * r; BIGNUM * s; /* A correct DER-encoded signature has the following form: 0x30: a header byte indicating a compound structure. A 1-byte length descriptor for all what follows. 0x02: a header byte indicating an integer. A 1-byte length descriptor for the R value The R coordinate, as a big-endian integer. 0x02: a header byte indicating an integer. A 1-byte length descriptor for the S value. The S coordinate, as a big-endian integer. */ r = BN_bin2bn( src+ 4, 32, NULL ); // create new bn here s = BN_bin2bn( src+ 4 +32 + 2, 32, NULL ); if(!BN_copy(sig-r, r)) goto err; if(!BN_copy(sig-s, s)) goto err; That wont always work because the number of octets in the ASN1 Integer isn't always the same. The ASN1 function d2i_ECDSA_SIG will corerectly parse the output. Steve. -- Dr Stephen N. Henson. OpenSSL project core developer. Commercial tech support now available see: http://www.openssl.org __ OpenSSL Project http://www.openssl.org User Support Mailing Listopenssl-users@openssl.org Automated List Manager majord...@openssl.org
Re: How to extract ECC signature bytes from EVP_DigestSignFinal's signature
On Tue, Mar 18, 2014 at 1:02 PM, axisofevil douglas.b...@ceiva.com wrote:
I dug into source - it's in DER format so a sleezy hacked function is this: (
I use curve NID_X9_62_prime256v1 )
ECDSA_SIG * sig
BIGNUM * r;
BIGNUM * s;
/* A correct DER-encoded signature has the following form:
0x30: a header byte indicating a compound structure.
A 1-byte length descriptor for all what follows.
0x02: a header byte indicating an integer.
A 1-byte length descriptor for the R value
The R coordinate, as a big-endian integer.
0x02: a header byte indicating an integer.
A 1-byte length descriptor for the S value.
The S coordinate, as a big-endian integer.
*/
r = BN_bin2bn( src+ 4, 32, NULL ); // create new bn here
s = BN_bin2bn( src+ 4 +32 + 2, 32, NULL );
if(!BN_copy(sig-r, r)) goto err;
if(!BN_copy(sig-s, s)) goto err;
Be aware you can have one of two formats depending on your platform
and they dont interop on their own.
First is the signature format of IEEE P1363, which is a simple
concatenation of {r,s}. If the has is 20 bytes, then the signature is
40 bytes. Its used by OpenPGP, Crypto++, etc.
Second is the DER encoding:
SEQUENCE ::= {
r INTEGER,
s INTEGER }
It is used by OpenSSL, Java, etc.
Jeff
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How to extract ECC signature bytes from EVP_DigestSignFinal's signature
I had been using the lower level ECDSA_do_sign for EC signing but had to migrate to EVP functions. If I get signature from EVP_DigestSignFinal(), what format is the signature, and how can I extract the 'real' bytes? I'd expect 32 bytes each for r and s. I need the 'real bytes' for compatibility. Thanks, dB -- View this message in context: http://openssl.6102.n7.nabble.com/How-to-extract-ECC-signature-bytes-from-EVP-DigestSignFinal-s-signature-tp48878.html Sent from the OpenSSL - User mailing list archive at Nabble.com. __ OpenSSL Project http://www.openssl.org User Support Mailing Listopenssl-users@openssl.org Automated List Manager majord...@openssl.org
