B4X Requires Chilkat v11.0.0+

Duplicating OpenSSL rsautl (creating RSA signatures)

See more RSA Examples

Demonstrates how to duplicate OpenSSL rsautil RSA signatures.

The Chilkat RSA component's methods for creating RSA signatures (SignBytes, SignBytesENC, SignString, and SignStringENC) are very different from OpenSSL's rsautl command. First, we'll explain what Chilkat's signing methods do, and then what OpenSSL's rsautl does. New signing methods have been added to Chilkat RSA to duplicate OpenSSL rsautl: OpenSslSignBytes, OpenSslSignBytesENC, OpenSslSignString, and OpenSslSignStringENC.

Here's what Chilkat's RSA Sign* methods do:
(Note: Chilkat RSA's Sign* methods generate signatures according to RSA Laboratories' "PKCS #1 v2.0: RSA Cryptography Standard".)

1. Input data is hashed using the hashing algorithm specified.
2. The hash is padded using either PKCS1 v1.5 or PKCS1 PSS padding. PKCS v1.5 involves encoding to ASN.1 before padding.
3. The padded hash is finally RSA signed (i.e. modular exponentiation) and the signature is returned.

OpenSSL rsautl is very different. Here's what it does:

1. The input data is not hashed. It must be a small enough amount of data such that it can be padded and signed. PKCS v1.5 padding is always used. The data is not ASN.1 encoded before padding.
2. The PKCS v1.5 padded data is RSA signed and the signature is returned.

The new OpenSsl* methods are designed to duplicate OpenSSL's rsautil signature functionality. B4X

Dim success As Boolean = False

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

Dim privKey As ChilkatPrivateKey
privKey.Initialize("privKey")

'  Load the private key from an RSA PEM file:
success = privKey.LoadPemFile("private.pem")
If success = False Then
    Log(privKey.LastErrorText)
    Return
End If


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


Dim strData As String = "secret"
Dim bd As ChilkatBinData
bd.Initialize
bd.AppendString(strData, "utf-8")

success = rsa.SignRawBd(bd)
Dim hexSig As String = bd.GetEncoded("hex")
Log(hexSig)

'  Recover the data using the corresponding public key:
Dim pubKey As ChilkatPublicKey
pubKey.Initialize

'  Load the public key from a PEM file:
success = pubKey.LoadFromFile("public.pem")
If success = False Then
    Log(pubKey.LastErrorText)
    Return
End If


Dim rsa2 As ChilkatRsa
rsa2.Initialize
success = rsa2.UsePublicKey(pubKey)
If success = False Then
    Log(rsa2.LastErrorText)
    Return
End If


Dim bd2 As ChilkatBinData
bd2.Initialize
bd2.AppendEncoded(hexSig, "hex")

'  Recover the original data.
success = rsa2.VerifyRawBd(bd2)
If success = False Then
    Log(rsa2.LastErrorText)
    Return
End If


Dim originalData As String = bd2.GetString("utf-8")
Log(originalData)