Lua Requires Chilkat v11.0.0+

RSA Encryption -- Same Key Different Results

See more RSA Examples

The RSA encryption algorithm produces different results for each call, even when encrypting the same data with the same key. Decryption however, will produce the correct results. This example demonstrates.

*** The reason this occurs is that RSA encryption uses PKCS1 v1.5 padding, and this padding scheme uses random bytes. It is random bytes in the padding that causes the result to be different each time.

Lua

local chilkat = require("chilkat")

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

local rsa = chilkat.Rsa.new()

local pubKeyXml = "<RSAPublicKey><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>"

local privKeyXml = "<RSAKeyValue><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent><P>4cpW9fvG99Jsz8/AO7PDHTl+pPRAglksrR2kClLV2g9DEeFe/bvmCxLUgMCJ+0eGQ1zA6aA7McKr13zTQ7jKpQ==</P><Q>4cCS/kFlq/P1ExF37Fkh4pCodOEGutepLEG7Q/KljT3ZGlAY+2l8fGu4f+hrkUuGoFl7NOMaJflULoPIgQaq/Q==</Q><DP>lkjcSsvzqh3YKRXJiLNkyf3rypV8noYGU4+oEOsDxilkZfFRDafUPUiiQrRk4ui/d/SzvozU+ZDuWfaOk8PatQ==</DP><DQ>SYCD25i7W8Mwdibn3uIecEAdOQDTSh5RjIFSUYs9b8FFYJXXrHPp/jCsf6jS7RmkGa1Iui1/JAIL8KEjtS7QmQ==</DQ><InverseQ>EDAJa3TpNdPQ3GIdBpnTgFTQY5A60DcszsUW/iCYoXQdPVJ9BLBxVTe9jiLzGuNuzLkVBwQlCy0Bf84hACRV9A==</InverseQ><D>cMFdDYKkddlRNczaugOmOH8b1egpx2liSPs6GYZ2gFObAXJiPK8m+r6c2ckls7hrlUP0DZhi4cG6Tn7xANb0Ek17P7QquVhQYOmFy/YHzm+IJbcwwq7pJHhZBhtcjyXqfUZ+BADGE//GQbrSVwVltpOj5KcxG88NAprLn2MMxfE=</D></RSAKeyValue>"

local pubKey = chilkat.PublicKey.new()
local success = pubKey:load_from_string(pubKeyXml)
if not success then
    print(pubKey.last_error_text)
    return
end

local privKey = chilkat.PrivateKey.new()
success = privKey:load_xml(privKeyXml)
if not success then
    print(privKey.last_error_text)
    return
end

success = rsa:use_public_key(pubKey)
if not success then
    print(rsa.last_error_text)
    return
end

-- Encrypt a string and return the encrypted data base64-encoded:
rsa.encoding_mode = "base64"

local plainText = "RSA gives different results with each call, weird but OK"

local usePrivateKey = false
local encryptedStr1 = rsa:encrypt_string_enc(plainText, usePrivateKey)
print(encryptedStr1)

-- Do it again. The results are different...
local encryptedStr2 = rsa:encrypt_string_enc(plainText, usePrivateKey)
print(encryptedStr2)

-- Now decrypt both strings, and the results are correct
-- in both cases:
local rsa2 = chilkat.Rsa.new()
success = rsa2:use_private_key(privKey)
if not success then
    print(rsa.last_error_text)
    return
end

rsa2.encoding_mode = "base64"
usePrivateKey = true

local decryptedStr1 = rsa2:decrypt_string_enc(encryptedStr1, usePrivateKey)
print(decryptedStr1)

local decryptedStr2 = rsa2:decrypt_string_enc(encryptedStr2, usePrivateKey)
print(decryptedStr2)