B4X Requires Chilkat v11.0.0+

Verfies an RSA Signature

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Verifies an RSA signature against the original data. B4X

Dim success As Boolean = False

'  The following data was signed by the following example:
'  RSA Sign using a Private Key on a USB Token or Smartcard
Dim bd As ChilkatBinData
bd.Initialize
Dim i As Int
For i = 0 To 100
    bd.AppendEncoded("000102030405060708090A0B0C0D0E0F", "hex")
Next

'  Load the signature
Dim bdSig As ChilkatBinData
bdSig.Initialize
success = bdSig.LoadFile("rsaSignatures/test1.sig")
If success = False Then
    Log("Failed to load the RSA signature")
    Return
End If


'  Get the public key to be used for signature verification.
Dim pubKey As ChilkatPublicKey
pubKey.Initialize
success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
If success = False Then
    Log(pubKey.LastErrorText)
    Return
End If


Dim rsa As ChilkatRsa
rsa.Initialize
success = rsa.UsePublicKey(pubKey)
If success = False Then
    Log(rsa.LastErrorText)
    Return
End If


'  Verify the hash of the data against the signature.
'  We pass in the original data.  Internally, the hash is generated
'  and used to validate the signature.
'  Validating the RSA signature means two things:  
'  (1) the original data is exactly what was signed, and 
'  (2) it was signed by the owner of the RSA private key.
success = rsa.VerifyBd(bd, "sha256", bdSig)

If success = False Then
    Log(rsa.LastErrorText)
    Log("Signature invalid.")
Else
    Log("Signature valid.")
End If