(Lianja) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat Lianja Extension Download Chilkat Lianja Extension

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

loPubkey = createobject("CkPublicKey")

loSbPem = createobject("CkStringBuilder")
llBCrlf = .T.
loSbPem.AppendLine("-----BEGIN PUBLIC KEY-----",llBCrlf)
loSbPem.AppendLine("MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF",llBCrlf)
loSbPem.AppendLine("3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA",llBCrlf)
loSbPem.AppendLine("04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s",llBCrlf)
loSbPem.AppendLine("Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF",llBCrlf)
loSbPem.AppendLine("wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE",llBCrlf)
loSbPem.AppendLine("f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W",llBCrlf)
loSbPem.AppendLine("SwIDAQAB",llBCrlf)
loSbPem.AppendLine("-----END PUBLIC KEY-----",llBCrlf)

// Load the public key object from the PEM. 
llSuccess = loPubkey.LoadFromString(loSbPem.GetAsString())
if (llSuccess <> .T.) then
    ? loPubkey.LastErrorText
    release loPubkey
    release loSbPem
    return
endif

// Build a small string to encrypt
loJson = createobject("CkJsonObject")
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 

loRsa = createobject("CkRsa")
loRsa.OaepPadding = .T.
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.
llBUsePrivateKey = .F.
lcEncryptedStr = loRsa.EncryptStringENC(loJson.Emit(),llBUsePrivateKey)
if (loRsa.LastMethodSuccess <> .T.) then
    ? loRsa.LastErrorText
    release loPubkey
    release loSbPem
    release loJson
    release loRsa
    return
endif

? "Result: " + lcEncryptedStr


release loPubkey
release loSbPem
release loJson
release loRsa