Hi, Thanks for your response. I'm sure that I only have the x-coordinate and when I reed up on ecc, it seems to be possible to verify the signature by only using this x-coordinate. Is there a way to do this with OpenSSL?
Br, Jonas 2013/9/3 Matt Caswell <fr...@baggins.org> > On 3 September 2013 15:16, Jonas Andersson <jonasanderssonm...@gmail.com> > wrote: > > Hi all, > > > > Is there a way to verify a signature with ECDSA_do_verify having only the > > x-coordinate (in public key) available? > > Are you sure you *only* have the x-coord and not a point in compressed > format? The difference being that with compressed format you get an > octet at the front specifying which of the two possible y values to > use (the y bit) followed by the full octets for the x coordinate. > > If you have it in compressed format as an octet string there are > functions to load it. You need to make sure that the point conversion > form for the curve is POINT_CONVERSION_COMPRESSED. You can set this > using EC_GROUP_set_point_conversion_form (not sure off the top of my > head what the default is for this). You can then load your compressed > point using EC_POINT_oct2point. > > Alternatively you can use EC_POINT_set_compressed_coordinates_GFp or > EC_POINT_set_compressed_coordinates_GF2m (for prime curves or binary > curves as appropriate). > > Hope that helps, > > Matt > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List openssl-users@openssl.org > Automated List Manager majord...@openssl.org >
