B4X Requires Chilkat v11.0.0+

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. B4X

Dim success As Boolean = False

'  This example assumes the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

'  Let's say you have a file containing the 32-bytes of a SHA256 hash,
'  and a file that is an RSA signature of those 32 bytes.
'  Here's how you verify using the RSA public key found in a PEM.

Dim pubKey As ChilkatPublicKey
pubKey.Initialize
success = pubKey.LoadFromFile("rsaPubKey.pem")
If success = False Then
    Log(pubKey.LastErrorText)
    Return
End If


Dim rsa As ChilkatRsa
rsa.Initialize

'  Get the public key.
success = rsa.UsePublicKey(pubKey)
If success = False Then
    Log(rsa.LastErrorText)
    Return
End If


'  Get the 32-byte SHA256 hash.
Dim bdHash As ChilkatBinData
bdHash.Initialize
success = bdHash.LoadFile("myHash.sha256")
If success = False Then
    Log("Failed to load SHA256 hash.")
    Return
End If


'  Get the RSA signature to be validated.
Dim bdSig As ChilkatBinData
bdSig.Initialize
success = bdSig.LoadFile("mySig.sig")
If success = False Then
    Log("Failed to load RSA signature.")
    Return
End If


'  Verify the signature against the SHA256 hash.
Dim enc As String = "base64"
rsa.EncodingMode = enc
success = rsa.VerifyHashENC(bdHash.GetEncoded(enc), "sha256", bdSig.GetEncoded(enc))
If success = False Then
    Log(rsa.LastErrorText)
    Return
End If


Log("Signature validated.")