(Excel) ECDSA Sign Data and Verify Signature

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

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' 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 Chilkat.Crypt2
Set crypt = Chilkat.NewCrypt2
crypt.HashAlgorithm = "SHA256"
crypt.Charset = "utf-8"
crypt.EncodingMode = "base64"

' Hash a string.

hash1 = crypt.HashStringENC("The quick brown fox jumps over the lazy dog")
Debug.Print "hash1 = "; hash1

' Or hash a file..

hash2 = crypt.HashFileENC("qa_data/hamlet.xml")
Debug.Print "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 Chilkat.PrivateKey
Set privKey = Chilkat.NewPrivateKey

success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If (success <> True) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
End If

' We'll need a PRNG source for random number generation.
' Use Chilkat's PRNG (for the Fortuna PRNG algorithm).
Dim prng As Chilkat.Prng
Set prng = Chilkat.NewPrng

' Sign the hash..
Dim ecdsa As Chilkat.Ecc
Set ecdsa = Chilkat.NewEcc

ecdsaSigBase64 = ecdsa.SignHashENC(hash1,"base64",privKey,prng)
If (ecdsa.LastMethodSuccess <> True) Then
    Debug.Print ecdsa.LastErrorText
    Exit Sub
End If

Debug.Print "ECDSA signature = "; ecdsaSigBase64

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

Dim pubKey As Chilkat.PublicKey
Set pubKey = Chilkat.NewPublicKey
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
If (success <> True) Then
    Debug.Print pubKey.LastErrorText
    Exit Sub
End If


result = ecdsa.VerifyHashENC(hash1,ecdsaSigBase64,"base64",pubKey)
If (result = 1) Then
    Debug.Print "Signature is valid."
    Exit Sub
End If

If (result = 0) Then
    Debug.Print "Signature is invalid."
    Exit Sub
End If

If (result < 0) Then
    Debug.Print ecdsa.LastErrorText
    Debug.Print "The VerifyHashENC method call failed."
    Exit Sub
End If