Objective-C

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.

Objective-C

#import <CkoRsa.h>
#import <NSString.h>
#import <CkoPublicKey.h>
#import <CkoPrivateKey.h>

BOOL success = NO;

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

CkoRsa *rsa = [[CkoRsa alloc] init];

NSString *pubKeyXml = @"<RSAPublicKey><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>";

NSString *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>";

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
success = [pubKey LoadFromString: pubKeyXml];
if (success == NO) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

CkoPrivateKey *privKey = [[CkoPrivateKey alloc] init];
success = [privKey LoadXml: privKeyXml];
if (success == NO) {
    NSLog(@"%@",privKey.LastErrorText);
    return;
}

success = [rsa UsePublicKey: pubKey];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

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

NSString *plainText = @"RSA gives different results with each call, weird but OK";

BOOL usePrivateKey = NO;
NSString *encryptedStr1 = [rsa EncryptStringENC: plainText bUsePrivateKey: usePrivateKey];
NSLog(@"%@",encryptedStr1);

// Do it again. The results are different...
NSString *encryptedStr2 = [rsa EncryptStringENC: plainText bUsePrivateKey: usePrivateKey];
NSLog(@"%@",encryptedStr2);

// Now decrypt both strings, and the results are correct
// in both cases:
CkoRsa *rsa2 = [[CkoRsa alloc] init];
success = [rsa2 UsePrivateKey: privKey];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

rsa2.EncodingMode = @"base64";
usePrivateKey = YES;

NSString *decryptedStr1 = [rsa2 DecryptStringENC: encryptedStr1 bUsePrivateKey: usePrivateKey];
NSLog(@"%@",decryptedStr1);

NSString *decryptedStr2 = [rsa2 DecryptStringENC: encryptedStr2 bUsePrivateKey: usePrivateKey];
NSLog(@"%@",decryptedStr2);