(Visual Basic 6.0) Verify an RSA Signature Against the Signed Hash

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Demonstrates how to validate an RSA Signature against the hash that was signed.

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

Dim bd As New ChilkatBinData
Dim i As Long
For i = 0 To 100
    success = bd.AppendEncoded("000102030405060708090A0B0C0D0E0F","hex")
Next
Dim sha256_base64 As String
sha256_base64 = bd.GetHash("sha256","base64")
Debug.Print "sha256 hash in base64 format: " & sha256_base64

Dim base64_rsa_sig As String
base64_rsa_sig = "AwF2BbOvL6jA5DwmMAc9n6J2Cc8PI6Rj5W079+aKJcIEtPWRzHor0Bvc3aftGM3Jbgj6SXlIC3M3RYS7UZOnfiHKFNZgbxaNT5WwsWooK42ZkC8DBZl0p7OunBUKd5SciUo+TKilioeUkriN3L1Zl9hwi3HVDVqgVo3XXskwIftSqLSFlepTLTmOWj9Y93dp8J4D9RyLtNgFQBc0WB22tyJTsuY56mLcWe1AMF3LizB9OrbwjynF2u16xWlrJdugccz795fJBUV9aQSD+8S3KeqwQhoi8RK1uhD68aGCyaSpBq0NZ8COAkn7MXaF4POxrAAt8udfHM+PRfSOptcH/w=="

' Get the public key to be used for signature verification.
Dim pubKey As New PublicKey
Dim success As Long
success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
If (success = 0) Then
    Debug.Print pubKey.LastErrorText
    Exit Sub
End If

Dim rsa As New ChilkatRsa
success = rsa.ImportPublicKeyObj(pubKey)

' Verify the hash against the signature.
rsa.EncodingMode = "base64"
success = rsa.VerifyHashENC(sha256_base64,"sha256",base64_rsa_sig)

If (success = 0) Then
    Debug.Print rsa.LastErrorText
    Debug.Print "Signature invalid."
Else
    Debug.Print "Signature valid."
End If