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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.

Lianja

llSuccess = .F.

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

loRsa = createobject("CkRsa")

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

lcPrivKeyXml = "<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>"

loPubKey = createobject("CkPublicKey")
llSuccess = loPubKey.LoadFromString(lcPubKeyXml)
if (llSuccess = .F.) then
    ? loPubKey.LastErrorText
    release loRsa
    release loPubKey
    return
endif

loPrivKey = createobject("CkPrivateKey")
llSuccess = loPrivKey.LoadXml(lcPrivKeyXml)
if (llSuccess = .F.) then
    ? loPrivKey.LastErrorText
    release loRsa
    release loPubKey
    release loPrivKey
    return
endif

llSuccess = loRsa.UsePublicKey(loPubKey)
if (llSuccess = .F.) then
    ? loRsa.LastErrorText
    release loRsa
    release loPubKey
    release loPrivKey
    return
endif

// Encrypt a string and return the encrypted data base64-encoded:
loRsa.EncodingMode = "base64"

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

llUsePrivateKey = .F.
lcEncryptedStr1 = loRsa.EncryptStringENC(lcPlainText,llUsePrivateKey)
? lcEncryptedStr1

// Do it again. The results are different...
lcEncryptedStr2 = loRsa.EncryptStringENC(lcPlainText,llUsePrivateKey)
? lcEncryptedStr2

// Now decrypt both strings, and the results are correct
// in both cases:
loRsa2 = createobject("CkRsa")
llSuccess = loRsa2.UsePrivateKey(loPrivKey)
if (llSuccess = .F.) then
    ? loRsa.LastErrorText
    release loRsa
    release loPubKey
    release loPrivKey
    release loRsa2
    return
endif

loRsa2.EncodingMode = "base64"
llUsePrivateKey = .T.

lcDecryptedStr1 = loRsa2.DecryptStringENC(lcEncryptedStr1,llUsePrivateKey)
? lcDecryptedStr1

lcDecryptedStr2 = loRsa2.DecryptStringENC(lcEncryptedStr2,llUsePrivateKey)
? lcDecryptedStr2


release loRsa
release loPubKey
release loPrivKey
release loRsa2