(Unicode C) RSA Encryption -- Same Key Different Results

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.

Chilkat C/C++ Library Downloads
MS Visual C/C++ Linux/CentOS C/C++ Alpine Linux C/C++ MAC OS X C/C++	armhf/aarch64 C/C++ C++ Builder iOS C/C++ Android C/C++	Solaris C/C++ MinGW C/C++

#include <C_CkRsaW.h>

void ChilkatSample(void)
    {
    HCkRsaW rsa;
    const wchar_t *publicKey;
    const wchar_t *privateKey;
    BOOL success;
    const wchar_t *plainText;
    BOOL usePrivateKey;
    const wchar_t *encryptedStr1;
    const wchar_t *encryptedStr2;
    HCkRsaW rsa2;
    const wchar_t *decryptedStr1;
    const wchar_t *decryptedStr2;

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

    rsa = CkRsaW_Create();

    // RSA public key in XML format:
    publicKey = L"<RSAPublicKey><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>";

    privateKey = L"<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>";

    success = CkRsaW_ImportPublicKey(rsa,publicKey);

    // Encrypt a string and return the encrypted data base64-encoded:
    CkRsaW_putEncodingMode(rsa,L"base64");

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

    usePrivateKey = FALSE;
    encryptedStr1 = CkRsaW_encryptStringENC(rsa,plainText,usePrivateKey);
    wprintf(L"%s\n",encryptedStr1);

    // Do it again. The results are different...
    encryptedStr2 = CkRsaW_encryptStringENC(rsa,plainText,usePrivateKey);
    wprintf(L"%s\n",encryptedStr2);

    // Now decrypt both strings, and the results are correct
    // in both cases:
    rsa2 = CkRsaW_Create();
    success = CkRsaW_ImportPrivateKey(rsa2,privateKey);
    CkRsaW_putEncodingMode(rsa2,L"base64");
    usePrivateKey = TRUE;

    decryptedStr1 = CkRsaW_decryptStringENC(rsa2,encryptedStr1,usePrivateKey);
    wprintf(L"%s\n",decryptedStr1);

    decryptedStr2 = CkRsaW_decryptStringENC(rsa2,encryptedStr2,usePrivateKey);
    wprintf(L"%s\n",decryptedStr2);


    CkRsaW_Dispose(rsa);
    CkRsaW_Dispose(rsa2);

    }