(PureBasic) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkStringBuilder.pb"
IncludeFile "CkJsonObject.pb"
IncludeFile "CkRsa.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

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

    pubkey.i = CkPublicKey::ckCreate()
    If pubkey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    sbPem.i = CkStringBuilder::ckCreate()
    If sbPem.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    bCrlf.i = 1
    CkStringBuilder::ckAppendLine(sbPem,"-----BEGIN PUBLIC KEY-----",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"SwIDAQAB",bCrlf)
    CkStringBuilder::ckAppendLine(sbPem,"-----END PUBLIC KEY-----",bCrlf)

    ; Load the public key object from the PEM. 
    success.i = CkPublicKey::ckLoadFromString(pubkey,CkStringBuilder::ckGetAsString(sbPem))
    If success <> 1
        Debug CkPublicKey::ckLastErrorText(pubkey)
        CkPublicKey::ckDispose(pubkey)
        CkStringBuilder::ckDispose(sbPem)
        ProcedureReturn
    EndIf

    ; Build a small string to encrypt
    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckUpdateString(json,"example","123")
    CkJsonObject::ckUpdateString(json,"hello","world")
    Debug CkJsonObject::ckEmit(json)

    ; 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 

    rsa.i = CkRsa::ckCreate()
    If rsa.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkRsa::setCkOaepPadding(rsa, 1)
    CkRsa::setCkOaepHash(rsa, "SHA-256")
    CkRsa::ckImportPublicKeyObj(rsa,pubkey)
    CkRsa::setCkEncodingMode(rsa, "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.
    bUsePrivateKey.i = 0
    encryptedStr.s = CkRsa::ckEncryptStringENC(rsa,CkJsonObject::ckEmit(json),bUsePrivateKey)
    If CkRsa::ckLastMethodSuccess(rsa) <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        CkPublicKey::ckDispose(pubkey)
        CkStringBuilder::ckDispose(sbPem)
        CkJsonObject::ckDispose(json)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    Debug "Result: " + encryptedStr


    CkPublicKey::ckDispose(pubkey)
    CkStringBuilder::ckDispose(sbPem)
    CkJsonObject::ckDispose(json)
    CkRsa::ckDispose(rsa)


    ProcedureReturn
EndProcedure