B4X Requires Chilkat v11.0.0+

RSA-OAEP with SHA256 hashing

See more RSA Examples

RSA encrypt a SHA256 hash with OAEP padding. 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 pubkey As ChilkatPublicKey
pubkey.Initialize

Dim sbPem As ChilkatStringBuilder
sbPem.Initialize
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. 
success = pubkey.LoadFromString(sbPem.GetAsString)
If success = False Then
    Log(pubkey.LastErrorText)
    Return
End If


'  Build a small string to encrypt
Dim json As ChilkatJsonObject
json.Initialize
json.UpdateString("example", "123")
json.UpdateString("hello", "world")
Log(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 ChilkatRsa
rsa.Initialize
rsa.PkcsPadding = False
rsa.OaepHash = "SHA-256"
rsa.UsePublicKey(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 = False Then
    Log(rsa.LastErrorText)
    Return
End If


Log("Result: " & encryptedStr)