Lianja

ECDSA Sign Data and Get Raw R and S Values

See more ECC Examples

Demonstrates getting the raw R and S value of an ECDSA signature. Lianja

llSuccess = .F.

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// To create an ECDSA signature, the data first needs to be hashed.  Then the hash
// is signed.

loCrypt = createobject("CkCrypt2")
loCrypt.HashAlgorithm = "SHA256"
loCrypt.Charset = "utf-8"
loCrypt.EncodingMode = "base64"

// Hash a string.
lcHash1 = loCrypt.HashStringENC("The quick brown fox jumps over the lazy dog")
? "hash1 = " + lcHash1

// -----------------------------------------------------------
// An ECDSA private key is used for signing.  The public key is for signature verification.
// Load our ECC private key.
// Our private key file contains this:

// 	// -----BEGIN PRIVATE KEY-----
// 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
// 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
// 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
// 	-----END PRIVATE KEY-----

loPrivKey = createobject("CkPrivateKey")
llSuccess = loPrivKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
if (llSuccess <> .T.) then
    ? loPrivKey.LastErrorText
    release loCrypt
    release loPrivKey
    return
endif

// Sign the hash..
loPrng = createobject("CkPrng")
loEcdsa = createobject("CkEcc")
lcEcdsaSigBase64 = loEcdsa.SignHashENC(lcHash1,"base64",loPrivKey,loPrng)
if (loEcdsa.LastMethodSuccess <> .T.) then
    ? loEcdsa.LastErrorText
    release loCrypt
    release loPrivKey
    release loPrng
    release loEcdsa
    return
endif

// The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
// For example:
// SEQUENCE (2 elem)
//   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
//   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

? "Base64 ECDSA signature = " + lcEcdsaSigBase64

// If the raw R and S values are needed, here's how to get them:
loAsn = createobject("CkAsn")
llSuccess = loAsn.LoadEncoded(lcEcdsaSigBase64,"base64")
if (llSuccess = .F.) then
    ? loAsn.LastErrorText
    release loCrypt
    release loPrivKey
    release loPrng
    release loEcdsa
    release loAsn
    return
endif

// The R and X will be in hexidecimal in the XML.
loXml = createobject("CkXml")
loXml.LoadXml(loAsn.AsnToXml())
? loXml.GetXml()

// The XML looks like this:
// <sequence>
// <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
// <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
// </sequence>

// Copy raw R and S hex values into a Chilkat BinData object.
loBd = createobject("CkBinData")
r = loXml.GetChildContent("int[0]")
s = loXml.GetChildContent("int[1]")
loBd.AppendEncoded(r,"hex")
loBd.AppendEncoded(s,"hex")

? "Number of bytes in bd: " + str(loBd.NumBytes)


release loCrypt
release loPrivKey
release loPrng
release loEcdsa
release loAsn
release loXml
release loBd