RSA将iOS转移到Java

Question

I want to encrypt a String in Objective-C (iOS) and decrypt it after HTTP Transfer in Java.

The Public Key was successfully transmitted from Java to iOS (at least it is recognied in the Keychain)

In ObjC I try to send the text "Hallo" using this:

NSData* myData = [@"Hallo" dataUsingEncoding:NSUTF8StringEncoding];
OSStatus status = noErr;    
size_t cipherBufferSize;
uint8_t *cipherBuffer;
cipherBufferSize = SecKeyGetBlockSize(publicKey);
cipherBuffer = malloc(cipherBufferSize);    
size_t dataLength = [self length];
uint8_t* intDataToEncrypt = (uint8_t*)[self bytes];
if (cipherBufferSize < dataLength) {
    printf("Could not encrypt.  Packet too large.\n");
    return NULL;
}
status = SecKeyEncrypt(    publicKey,
                       kSecPaddingNone,
                       intDataToEncrypt,
                       dataLength,
                       cipherBuffer,
                       &cipherBufferSize
                       );
NSData *encryptedData = [NSData dataWithBytes:cipherBuffer length:cipherBufferSize];

"encryptedData" is then send base64 encoded via HTTP Post to a Java Servlet which uses this (BouncyCastle is used and the data converted back from Base64 first, the key is read from a file):

PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(b64.decodeBuffer(key));
PrivateKey privateKey = kf.generatePrivate(keySpec);
Cipher cipher = Cipher.getInstance("RSA/NONE/NoPadding");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] myData = cipher.doFinal(byteData, 0, 256);

The output is completely messed up when trying to use as new String(myData, "UTF-8"); I tried sending only the "Hallo" without encryption this works, so it seems base64 is ok. When I encrypt the same phrase in Java directly the output differs in 2 Bytes from the ObjC encryption.

In the End I want to use OAEP Padding instead of none...

I hope someone can help with this, the iOS Security Framework seems really to be very bad

Answer 1

The Problem was not in the RSA part but the Base64 encoding and transfer. All "+" in the String were received as " " due to HTTP(S) transfer (of course, I should have thought of that).

Replacing them with "-" as proposed by the unofficial Base64URL version solves the problem. (also all "/" with "_")

This also explain why only 2 bytes were different - those were the "+" symbol bytes.