Hello Jeff,
that value is constructed following this standard
https://tools.ietf.org/id/draft-jivsov-ecc-compact-00.xml#NIST-SP800-133 , but
unfortunately I cannot assume any other assumptions.
Luca
Jeffrey Walton <noloa...@gmail.com> ha scritto:
On Tuesday, February 5, 2019 at 9:56:44 AM UTC-5, luca.d...@cnit.it wrote:
Hello,
I'm implementing a security daemon on the vehicular communication scope.
I could receive a message with a signature and the compressed X coordinate
of a point to verify that signature. The elliptic curve can be either the
secp256 or the brainpoolp256r1 and the algorithm is ECDSA.
My question is: how can I recover the ECC Point (and so the public key)
given only the compressed X coordinate?
I followed some links which explain it (and many others)
https://www.cryptopp.com/wiki/Point_Compression
https://stackoverflow.com/questions/16576434/crypto-and-compressed-ec-keys
but they don't fit my problem.
I tried to produce code to resolve the problem (
https://pastebin.com/JFLxuW1X
<https://www.google.com/url?q=https%3A%2F%2Fpastebin.com%2FJFLxuW1X&sa=D&sntz=1&usg=AFQjCNEfB2oA3V5N9_a0HktwAWpAGiQVJw>)
but it doesn't work.
Please show how this value is constructed:
string compactPoint =
"937120662418500f3ad7c892b1db7e7c2d85ec48c74e99d64dcb7083082bb4f3";
Jeff
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