Sample code for 30+ languages & platforms
Visual Basic 6.0

Duplicate openssl dgst -md5 -sign myKey.pem something.txt | openssl enc -base64 -A

See more RSA Examples

Demonstrates how to duplicate the creation of an RSA signature produced by this OpenSSL command:
openssl dgst -md5 -sign myKey.pem something.txt | openssl enc -base64 -A

Chilkat Visual Basic 6.0 Downloads

Visual Basic 6.0
Dim success As Long
success = 0

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

Dim pkey As New PrivateKey

' Load the private key from an RSA PEM file:
success = pkey.LoadPemFile("myKey.pem")

Dim rsa As New ChilkatRsa

' Import the private key into the RSA component:
success = rsa.UsePrivateKey(pkey)
If (success = 0) Then
    Debug.Print rsa.LastErrorText
    Exit Sub
End If

' OpenSSL uses BigEndian byte ordering:
rsa.LittleEndian = 0

' The resulting signature will be a Base64 string:
rsa.EncodingMode = "base64"

' For simplicity, we're not loading
' the data to be signed from a file.  We are instead simply
' using a literal string value.  
Dim strData As String
strData = "This is the text to be signed."

' Hash the input using MD5, and then sign the hash:
' Other valid hash algorithm choices are "md2" and "sha-1".
Dim base64Sig As String
base64Sig = rsa.SignStringENC(strData,"md5")

Debug.Print base64Sig

Debug.Print "Success!"