B4X Requires Chilkat v11.0.0+

Duplicate openssl rsautl -encrypt –in mytext.txt -out mytest.enc -inkey mycertificate.cer -certin –pkcs

See more OpenSSL Examples

Demonstrates how to duplicate this OpenSSL command:

openssl.exe  rsautl -encrypt –in mytext.txt -out mytest.enc -inkey mycertificate.cer -certin –pkcs

Important: The RSA encryption algorithm produces different results for each call, even when encrypting the same data with the same key. Decryption however, will produce the correct results. This example demonstrates.

The reason this occurs is that RSA encryption uses PKCS1 v1.5 padding, and this padding scheme uses random bytes. It is random bytes in the padding that causes the result to be different each time.

The mytext.txt file is a small file. (RSA can only be used to encrypt or sign small amounts of data.)

How much data can be encrypted with "openssl rsautl"? The maximum size (in bytes) is the key size minus the overhead for the padding. The overhead size depends on the padding. With OAEP padding, the overhead is 42 bytes. With the default PKCSv1.5 padding, the overhead is 11 bytes.

Given a 2048-bit RSA key (256 bytes) and using PKCSv1.5 padding, the max data size that can be signed is 256 - 11 = 245 bytes.

B4X

Dim success As Boolean = False

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

Dim cert As ChilkatCert
cert.Initialize("cert")

'  Load the certificate from a file.
success = cert.LoadFromFile("mycertificate.cer")
If success = False Then
    Log(cert.LastErrorText)
    Return
End If


'  Load the file to be encrypted.
Dim bd As ChilkatBinData
bd.Initialize
success = bd.LoadFile("mytext.txt")

Dim rsa As ChilkatRsa
rsa.Initialize

'  Get the cert's public key.
Dim pubkey As ChilkatPublicKey
pubkey.Initialize
cert.GetPublicKey(pubkey)

'  Import the public key into the RSA component:
success = rsa.UsePublicKey(pubkey)
If success <> True Then
    Log(rsa.LastErrorText)
    Return
End If


'  OpenSSL uses big-endian.
rsa.LittleEndian = False

'  Encrypt the contents of bd, replacing it with the encrypted data.
Dim bUsePrivateKey As Boolean = False
success = rsa.EncryptBd(bd, bUsePrivateKey)
If success = False Then
    Log(rsa.LastErrorText)
    Return
End If


'  Save the RSA encrypted data to a file.
success = bd.WriteFile("mytest.enc")
If success <> True Then
    Log("Failed to write RSA encrypted output file.")
    Return
End If


Log("Success.")