(Visual FoxPro) ECDSA Sign Data and Get Raw R and S Values

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loCrypt
LOCAL lcHash1
LOCAL loPrivKey
LOCAL lnSuccess
LOCAL loPrng
LOCAL loEcdsa
LOCAL lcEcdsaSigBase64
LOCAL loAsn
LOCAL loXml
LOCAL loBd
LOCAL r
LOCAL s

* 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('Chilkat_9_5_0.Crypt2')
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('Chilkat_9_5_0.PrivateKey')
lnSuccess = loPrivKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
IF (lnSuccess <> 1) THEN
    ? loPrivKey.LastErrorText
    RELEASE loCrypt
    RELEASE loPrivKey
    CANCEL
ENDIF

* Sign the hash..
loPrng = CreateObject('Chilkat_9_5_0.Prng')
loEcdsa = CreateObject('Chilkat_9_5_0.Ecc')
lcEcdsaSigBase64 = loEcdsa.SignHashENC(lcHash1,"base64",loPrivKey,loPrng)
IF (loEcdsa.LastMethodSuccess <> 1) THEN
    ? loEcdsa.LastErrorText
    RELEASE loCrypt
    RELEASE loPrivKey
    RELEASE loPrng
    RELEASE loEcdsa
    CANCEL
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('Chilkat_9_5_0.Asn')
lnSuccess = loAsn.LoadEncoded(lcEcdsaSigBase64,"base64")
IF (lnSuccess = 0) THEN
    ? loAsn.LastErrorText
    RELEASE loCrypt
    RELEASE loPrivKey
    RELEASE loPrng
    RELEASE loEcdsa
    RELEASE loAsn
    CANCEL
ENDIF

* The R and X will be in hexidecimal in the XML.
loXml = CreateObject('Chilkat_9_5_0.Xml')
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('Chilkat_9_5_0.BinData')
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