(PowerBuilder) RSA Decrypt Binary

When something is RSA encrypted, the output is always equal in size to the RSA key. For example, if "Hello World" is encrypted with a 1024-bit RSA key, the output is 128 bytes (because 1024 bits / 8 bits per byte = 128 bytes). You can see that the size of the RSA key imposes a limit on how many bytes can be encrypted. Thus RSA encryption is for small amounts of data. A typical use for RSA encryption is to encrypt a bulk (symmetric) encryption key.

In this example, we have a binary file containing the result of RSA encryption. The size of the file tells us the RSA key size. For example, if the file is exactly 256 bytes, we know that the RSA key required to decrypt must be a 2048-bit key.

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

integer li_rc
oleobject loo_Rsa
oleobject loo_PrivKey
integer li_Success
oleobject loo_BdEncrypted
string ls_Passphrase

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

loo_Rsa = create oleobject
// Use "Chilkat_9_5_0.Rsa" for versions of Chilkat < 10.0.0
li_rc = loo_Rsa.ConnectToNewObject("Chilkat.Rsa")
if li_rc < 0 then
    destroy loo_Rsa
    MessageBox("Error","Connecting to COM object failed")
    return
end if

loo_PrivKey = create oleobject
// Use "Chilkat_9_5_0.PrivateKey" for versions of Chilkat < 10.0.0
li_rc = loo_PrivKey.ConnectToNewObject("Chilkat.PrivateKey")

li_Success = loo_PrivKey.LoadPemFile("myPrivateKey.pem")
if li_Success <> 1 then
    Write-Debug loo_PrivKey.LastErrorText
    destroy loo_Rsa
    destroy loo_PrivKey
    return
end if

li_Success = loo_Rsa.ImportPrivateKeyObj(loo_PrivKey)
if li_Success <> 1 then
    Write-Debug loo_Rsa.LastErrorText
    destroy loo_Rsa
    destroy loo_PrivKey
    return
end if

// Load the encrypted bytes.
// This will typically be a file that is 128, 256, etc. bytes in length.
// For example, maybe it is a file containing an encrypted passphrase...
loo_BdEncrypted = create oleobject
// Use "Chilkat_9_5_0.BinData" for versions of Chilkat < 10.0.0
li_rc = loo_BdEncrypted.ConnectToNewObject("Chilkat.BinData")

li_Success = loo_BdEncrypted.LoadFile("qa_data/passphrase.enc")
if li_Success <> 1 then
    Write-Debug "Failed to load file."
    destroy loo_Rsa
    destroy loo_PrivKey
    destroy loo_BdEncrypted
    return
end if

// In this case, we know that it was a string that was encrypted,
// so decryption should result in a string.
// To make things easy, we'll pass the RSA encrypted data as a Base64 string 
// to the decryptor.
loo_Rsa.EncodingMode = "base64"
ls_Passphrase = loo_Rsa.DecryptStringENC(loo_BdEncrypted.GetEncoded("base64"),1)
if loo_Rsa.LastMethodSuccess <> 1 then
    Write-Debug loo_Rsa.LastErrorText
    destroy loo_Rsa
    destroy loo_PrivKey
    destroy loo_BdEncrypted
    return
end if

Write-Debug "Decrypted passphrase: " + ls_Passphrase


destroy loo_Rsa
destroy loo_PrivKey
destroy loo_BdEncrypted