(Visual FoxPro) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loPubkey
LOCAL loSbPem
LOCAL lnBCrlf
LOCAL lnSuccess
LOCAL loJson
LOCAL loRsa
LOCAL lnBUsePrivateKey
LOCAL lcEncryptedStr

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PublicKey')
loPubkey = CreateObject('Chilkat.PublicKey')

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbPem = CreateObject('Chilkat.StringBuilder')
lnBCrlf = 1
loSbPem.AppendLine("-----BEGIN PUBLIC KEY-----",lnBCrlf)
loSbPem.AppendLine("MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF",lnBCrlf)
loSbPem.AppendLine("3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA",lnBCrlf)
loSbPem.AppendLine("04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s",lnBCrlf)
loSbPem.AppendLine("Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF",lnBCrlf)
loSbPem.AppendLine("wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE",lnBCrlf)
loSbPem.AppendLine("f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W",lnBCrlf)
loSbPem.AppendLine("SwIDAQAB",lnBCrlf)
loSbPem.AppendLine("-----END PUBLIC KEY-----",lnBCrlf)

* Load the public key object from the PEM. 
lnSuccess = loPubkey.LoadFromString(loSbPem.GetAsString())
IF (lnSuccess <> 1) THEN
    ? loPubkey.LastErrorText
    RELEASE loPubkey
    RELEASE loSbPem
    CANCEL
ENDIF

* Build a small string to encrypt
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJson = CreateObject('Chilkat.JsonObject')
loJson.UpdateString("example","123")
loJson.UpdateString("hello","world")
? loJson.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 

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rsa')
loRsa = CreateObject('Chilkat.Rsa')
loRsa.OaepPadding = 1
loRsa.OaepHash = "SHA-256"
loRsa.ImportPublicKeyObj(loPubkey)
loRsa.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.
lnBUsePrivateKey = 0
lcEncryptedStr = loRsa.EncryptStringENC(loJson.Emit(),lnBUsePrivateKey)
IF (loRsa.LastMethodSuccess <> 1) THEN
    ? loRsa.LastErrorText
    RELEASE loPubkey
    RELEASE loSbPem
    RELEASE loJson
    RELEASE loRsa
    CANCEL
ENDIF

? "Result: " + lcEncryptedStr

RELEASE loPubkey
RELEASE loSbPem
RELEASE loJson
RELEASE loRsa