Xbase++

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. Xbase++

LOCAL nSuccess
LOCAL oCrypt
LOCAL cHash1
LOCAL oPrivKey
LOCAL oPrng
LOCAL oEcdsa
LOCAL cEcdsaSigBase64
LOCAL oAsn
LOCAL oXml
LOCAL oBd
LOCAL r
LOCAL s

nSuccess := 0

//  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.

oCrypt := CreateObject("Chilkat.Crypt2")
oCrypt:HashAlgorithm := "SHA256"
oCrypt:Charset := "utf-8"
oCrypt:EncodingMode := "base64"

//  Hash a string.
cHash1 := oCrypt:HashStringENC("The quick brown fox jumps over the lazy dog")
? "hash1 = " + cHash1

//  -----------------------------------------------------------
//  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-----

oPrivKey := CreateObject("Chilkat.PrivateKey")
nSuccess := oPrivKey:LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
IF (nSuccess != 1)
    ? oPrivKey:LastErrorText
    oCrypt:destroy()
    oPrivKey:destroy()
    RETURN
ENDIF

//  Sign the hash..
oPrng := CreateObject("Chilkat.Prng")
oEcdsa := CreateObject("Chilkat.Ecc")
cEcdsaSigBase64 := oEcdsa:SignHashENC(cHash1, "base64", oPrivKey, oPrng)
IF (oEcdsa:LastMethodSuccess != 1)
    ? oEcdsa:LastErrorText
    oCrypt:destroy()
    oPrivKey:destroy()
    oPrng:destroy()
    oEcdsa:destroy()
    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 = " + cEcdsaSigBase64

//  If the raw R and S values are needed, here's how to get them:
oAsn := CreateObject("Chilkat.Asn")
nSuccess := oAsn:LoadEncoded(cEcdsaSigBase64, "base64")
IF (nSuccess == 0)
    ? oAsn:LastErrorText
    oCrypt:destroy()
    oPrivKey:destroy()
    oPrng:destroy()
    oEcdsa:destroy()
    oAsn:destroy()
    RETURN
ENDIF

//  The R and X will be in hexidecimal in the XML.
oXml := CreateObject("Chilkat.Xml")
oXml:LoadXml(oAsn:AsnToXml())
? oXml: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.
oBd := CreateObject("Chilkat.BinData")
r := oXml:GetChildContent("int[0]")
s := oXml:GetChildContent("int[1]")
oBd:AppendEncoded(r, "hex")
oBd:AppendEncoded(s, "hex")

? "Number of bytes in bd: " + Str(oBd:NumBytes)

oCrypt:destroy()
oPrivKey:destroy()
oPrng:destroy()
oEcdsa:destroy()
oAsn:destroy()
oXml:destroy()
oBd:destroy()