(VB.NET) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

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

Dim pubkey As New Chilkat.PublicKey

Dim sbPem As New Chilkat.StringBuilder
Dim bCrlf As Boolean = True
sbPem.AppendLine("-----BEGIN PUBLIC KEY-----",bCrlf)
sbPem.AppendLine("MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF",bCrlf)
sbPem.AppendLine("3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA",bCrlf)
sbPem.AppendLine("04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s",bCrlf)
sbPem.AppendLine("Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF",bCrlf)
sbPem.AppendLine("wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE",bCrlf)
sbPem.AppendLine("f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W",bCrlf)
sbPem.AppendLine("SwIDAQAB",bCrlf)
sbPem.AppendLine("-----END PUBLIC KEY-----",bCrlf)

' Load the public key object from the PEM. 
Dim success As Boolean = pubkey.LoadFromString(sbPem.GetAsString())
If (success <> True) Then
    Debug.WriteLine(pubkey.LastErrorText)
    Exit Sub
End If


' Build a small string to encrypt
Dim json As New Chilkat.JsonObject
json.UpdateString("example","123")
json.UpdateString("hello","world")
Debug.WriteLine(json.Emit())

' This is the JSON to be RSA encrypted:  {"example":"123","hello":"world"}

' IMPORTANT: RSA encryption is only used to encrypt small amounts of data.
' RSA is only able to encrypt data to a maximum amount of your key size (2048 bits = 256 bytes) 
' minus padding / header data (11 bytes for PKCS#1 v1.5 padding, 42 bytes for OAEP).
' As a result it is often not possible to encrypt files with RSA directly. 
' RSA is also not meant for this purpose. 
' 
' If you want to encrypt more data, you can use something like:
' 1) Generate a 256-bit random keystring K
' 2) Encrypt your data with AES-CBC with K
' 3) Encrypt K with RSA
' 4) Send both to the other side 

Dim rsa As New Chilkat.Rsa
rsa.OaepPadding = True
rsa.OaepHash = "SHA-256"
rsa.ImportPublicKeyObj(pubkey)
rsa.EncodingMode = "base64"

' Note: The OAEP padding uses random bytes in the padding, and therefore each time encryption happens,
' even using the same data and key, the result will be different --  but still valid.  One should not expect
' to get the same output.
Dim bUsePrivateKey As Boolean = False
Dim encryptedStr As String = rsa.EncryptStringENC(json.Emit(),bUsePrivateKey)
If (rsa.LastMethodSuccess <> True) Then
    Debug.WriteLine(rsa.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Result: " & encryptedStr)