B4X

ECDSA Sign Data and Verify Signature

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Demonstrates using the Elliptic Curve Digital Signature Algorithm to hash data and sign it. Also demonstrates how to verify the ECDSA signature. B4X

Dim success As Boolean = False

'  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.

'  Use Chilkat Crypt2 to generate a hash for any of the following
'  hash algorithms: SHA256, SHA384, SHA512, SHA1, MD5, MD2, HAVAL, RIPEMD128/160/256/320

Dim crypt As ChilkatCrypt2
crypt.Initialize("crypt")
crypt.HashAlgorithm = "SHA256"
crypt.Charset = "utf-8"
crypt.EncodingMode = "base64"

'  Hash a string.
Dim hash1 As String = crypt.HashStringENC("The quick brown fox jumps over the lazy dog")
Log("hash1 = " & hash1)

'  Or hash a file..
Dim hash2 As String = crypt.HashFileENC("qa_data/hamlet.xml")
Log("hash2 = " & hash2)

'  (The Crypt2 API provides many other ways to hash data..)

'  -----------------------------------------------------------
'  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-----

Dim privKey As ChilkatPrivateKey
privKey.Initialize("privKey")
success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If success <> True Then
    Log(privKey.LastErrorText)
    Return
End If


'  We'll need a PRNG source for random number generation.
'  Use Chilkat's PRNG (for the Fortuna PRNG algorithm).
Dim prng As ChilkatPrng
prng.Initialize

'  Sign the hash..
Dim ecdsa As ChilkatEcc
ecdsa.Initialize
Dim ecdsaSigBase64 As String = ecdsa.SignHashENC(hash1, "base64", privKey, prng)
If ecdsa.LastMethodSuccess <> True Then
    Log(ecdsa.LastErrorText)
    Return
End If


Log("ECDSA signature = " & ecdsaSigBase64)

'  -----------------------------------------------------------
'  Now let's verify the signature using the public key.

Dim pubKey As ChilkatPublicKey
pubKey.Initialize
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
If success <> True Then
    Log(pubKey.LastErrorText)
    Return
End If


Dim result As Int = ecdsa.VerifyHashENC(hash1, ecdsaSigBase64, "base64", pubKey)
If result = 1 Then
    Log("Signature is valid.")
    Return
End If

If result = 0 Then
    Log("Signature is invalid.")
    Return
End If

If result < 0 Then
    Log(ecdsa.LastErrorText)
    Log("The VerifyHashENC method call failed.")
    Return
End If