RSA_GetPublicKeyFromCert

Extracts a public key from an X.509 certificate.

VB6/VBA

Debug.Print "Testing RSA_GetPublicKeyFromCert ..."
Dim strCertFile As String
Dim strKeyFile As String
Dim strPublicKey As String
Dim nChars As Long
Dim nRet As Long

strCertFile = "AliceRSASignByCarl.cer"
' First find out the length of string we need
nChars = RSA_GetPublicKeyFromCert(vbNullString, 0, strCertFile, 0)
Debug.Print "RSA_GetPublicKeyFromCert returns " & nChars & " (expecting +ve)"
If nChars <= 0 Then
    Debug.Print "ERROR: " & pkiErrorLookup(nChars)
    Exit Sub
End If
' Pre-dimension the string to receive data - IMPORTANT
strPublicKey = String(nChars, " ")
' Read in the Public Key in our "internal" format
nRet = RSA_GetPublicKeyFromCert(strPublicKey, nChars, strCertFile, 0)
Debug.Print "Public key is " & RSA_KeyBits(strPublicKey) & " bits long"

' Now save as a PKCS#1 public key file
strKeyFile = "AlicePubRSA.pub"
nRet = RSA_SavePublicKey(strKeyFile, strPublicKey, 0)
Debug.Print "RSA_SavePublicKey returns " & nRet
If nRet = 0 Then
    Debug.Print "Saved as public key file '" & strKeyFile & "'"
Else
    Debug.Print "ERROR: " & pkiErrorLookup(nRet)
End If

Output

Testing RSA_GetPublicKeyFromCert ...
RSA_GetPublicKeyFromCert returns 220 (expecting +ve)
Public key is 1024 bits long
RSA_SavePublicKey returns 0
Saved as public key file 'AlicePubRSA.pub'

VB.NET

Console.WriteLine("Testing RSA_GetPublicKeyFromCert ...")
Dim strCertFile As String
Dim strKeyFile As String
Dim sbPublicKey As StringBuilder
Dim nRet As Integer

strCertFile = "AliceRSASignByCarl.cer"
sbPublicKey = Rsa.GetPublicKeyFromCert(strCertFile)
Console.WriteLine("RSA_GetPublicKeyFromCert returns " & sbPublicKey.Length & " (expecting +ve)")
If sbPublicKey.Length = 0 Then
    Console.WriteLine("ERROR: " & General.LastError())
    Exit Sub
End If
Console.WriteLine("Public key is " & Rsa.KeyBits(sbPublicKey.ToString()) & " bits long")

' Now save as a PKCS#1 public key file
strKeyFile = "AlicePubRSA.pub"
nRet = Rsa.SavePublicKey(strKeyFile, sbPublicKey.ToString(), 0)
Console.WriteLine("RSA_SavePublicKey returns " & nRet)
If nRet = 0 Then
    Console.WriteLine("Saved as public key file '" & strKeyFile & "'")
Else
    Console.WriteLine("ERROR: " & General.LastError())
End If

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