On Wed, Jul 03, 2013, phildoch wrote:
> I have a 96 bytes long ecdsa signature created with sha384 algorithm by a
> smart card in raw format.It is composed of two 48 bytes long integers r and
> s. The ecdsa signature is in a buffer pointed to by sign_ptr. I'm converting
> the raw format signature into buf_out in ASN1 format with this function (in
> C):
>
> int convert_ecdsa_sha384_sign(char **buf_out, char *sign_ptr)
> {
> buf_out[0]=0x30; /* Type = Sequence of */
> buf_out[2]=0x02; /* Type = Integer */
> /* Verify if negative bit is set */
> if (!(sign_ptr[0] & 0x80))
> {
> buf_out[3]=0x30; /* Length */
> memcpy(&(buf_out[4]), sign_ptr, 48); /* Copy first integer */
> }
> else
> {
> /* Negative bit is set. Add one padding byte */
> buf_out[3]=0x31; /* Length */
> buf_out[4]=0x00; /* Padding */
> memcpy(&(buf_out[5]), sign_ptr, 48); /* Copy first integer */
> sign_offset += 1;
> }
>
> buf_out[52+sign_offset]=0x02; /*
> Type = Integer */
> /* Verify if negative bit is set */
> if (!(sign_ptr[48] & 0x80))
> {
> buf_out[53+sign_offset]=0x30; /*
> Length */
> memcpy(((&(buf_out[54]))+ sign_offset), sign_ptr + 48, 48); /*
> Copy second integer */
> }
> else
> {
> /* Negative bit is set. Add one padding byte */
> buf_out[53+sign_offset]=0x31; /*
> Length */
> buf_out[54+sign_offset]=0x00; /*
> Padding */
> memcpy(((&(buf_out[55]))+ sign_offset), sign_ptr + 48, 48); /* Copy
> second integer */
> sign_offset += 1;
> }
> buf_out[1]= 100 + sign_offset; /*
> Total signature length */
> return 1;
>
> I am wondering if there is an equivalent openssl function that can help me
> to do this in a more elegant way? I did look at many d2i functions
> (d2i_ASN1_xxxx, ASN1_item_d2i, ASN_d2i_func, etc.) but it is not clear which
> one suits.
>
The structure ECDSA_SIG is the one you need.
In outline: allocate the structure using ECDSA_SIG_new, set the r and s values
using BN_bin2bn, encode the result with i2d_ECDSA_SIG and finally free with
ECDSA_SIG_free.
Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org
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