I’m developing a application for ios and Android. I’m relatively new to crypto tasks and for the last 3 Days I keep banging my head against the wall because I’m not able to get RSA encryption running.
Both clients receive a public key from a java server. In android i have (obviously, because it is almost the same code as on server side) no troubles, but the ios part seems to be not compatible at all. I want to encrypt a little piece of data (aes key) with the public key and this is how I do this in Java:
try {
String publickey = "MCwwDQYJKoZIhvcNAQEBBQADGwAwGAIRAK+dBpbOKw+1VKMWoFxjU6UCAwEAAQ==";
byte[] bArr = Crypto.base64Decode(publicKey, false);
KeyFactory keyFactory = KeyFactory.getInstance("RSA", "BC");
EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKey);
PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);
Cipher cipher = Cipher.getInstance("RSA/NONE/PKCS1Padding", "BC");
cipher.init(1,publicKey);
int cipherBlockSize = cipher.getBlockSize();
ByteArrayOutputStream bArrOut = new ByteArrayOutputStream();
bArrOut.flush();
int pos = 0;
Log.i("ContentBufferLength", contentBuffer.length+"");
while (true) {
if (cipherBlockSize > contentBuffer.length - pos) {
cipherBlockSize = contentBuffer.length - pos;
}
Log.i("CipherBlockSize", cipherBlockSize+"");
byte[] tmp = cipher.doFinal(contentBuffer, pos, cipherBlockSize);
bArrOut.write(tmp);
pos += cipherBlockSize;
if (contentBuffer.length <= pos) {
break;
}
}
bArrOut.flush();
encryptedBuffer = bArrOut.toByteArray();
bArrOut.close();
} catch (Exception ex) {
throw ex;
}
// Log.i("Encrypted Buffer Length", encryptedBuffer.length+"");
return encryptedBuffer;
And this is my (not properly working) ios code, borrowed from here:
http://blog.wingsofhermes.org/?p=75 and the apple crypto exercises.
-(NSString* )encryptWithPublicKey:(NSString*)key input:(NSString*) input {
const size_t BUFFER_SIZE = 16;
const size_t CIPHER_BUFFER_SIZE = 16;
//const uint32_t PADDING = kSecPaddingNone;
const uint32_t PADDING = kSecPaddingPKCS1;
static const UInt8 publicKeyIdentifier[] = "de.irgendwas.app";
NSData *publicTag;
publicTag = [[NSData alloc] initWithBytes:publicKeyIdentifier length:sizeof(publicKeyIdentifier)];
NSMutableDictionary *publicKey2 = [[NSMutableDictionary alloc] init];
[publicKey2 setObject:kSecClassKey forKey:kSecClass];
[publicKey2 setObject:kSecAttrKeyTypeRSA forKey:kSecAttrKeyType];
[publicKey2 setObject:publicTag forKey:kSecAttrApplicationTag];
SecItemDelete((CFDictionaryRef)publicKey2);
NSData *strippedPublicKeyData = [NSData dataFromBase64String:key];
unsigned char * bytes = (unsigned char *)[strippedPublicKeyData bytes];
size_t bytesLen = [strippedPublicKeyData length];
size_t i = 0;
if (bytes[i++] != 0x30)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
/* Skip size bytes */
if (bytes[i] > 0x80)
i += bytes[i] - 0x80 + 1;
else
i++;
if (i >= bytesLen)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
if (bytes[i] != 0x30)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
/* Skip OID */
i += 15;
if (i >= bytesLen - 2)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
if (bytes[i++] != 0x03)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
/* Skip length and null */
if (bytes[i] > 0x80)
i += bytes[i] - 0x80 + 1;
else
i++;
if (i >= bytesLen)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
if (bytes[i++] != 0x00)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
if (i >= bytesLen)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
strippedPublicKeyData = [NSData dataWithBytes:&bytes[i] length:bytesLen - i];
DLog(@"X.509 Formatted Public Key bytes:\n%@",[strippedPublicKeyData description]);
if (strippedPublicKeyData == nil)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
CFTypeRef persistKey = nil;
[publicKey2 setObject:strippedPublicKeyData forKey:kSecValueData];
[publicKey2 setObject: (kSecAttrKeyClassPublic) forKey:kSecAttrKeyClass];
[publicKey2 setObject:[NSNumber numberWithBool:YES] forKey:kSecReturnPersistentRef];
OSStatus secStatus = SecItemAdd((CFDictionaryRef)publicKey2, &persistKey);
if (persistKey != nil) CFRelease(persistKey);
if ((secStatus != noErr) && (secStatus != errSecDuplicateItem))
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
SecKeyRef keyRef = nil;
[publicKey2 removeObjectForKey:kSecValueData];
[publicKey2 removeObjectForKey:kSecReturnPersistentRef];
[publicKey2 setObject:[NSNumber numberWithBool:YES] forKey:kSecReturnRef];
[publicKey2 setObject: kSecAttrKeyTypeRSA forKey:kSecAttrKeyType];
SecItemCopyMatching((CFDictionaryRef)publicKey2,(CFTypeRef *)&keyRef);
if (!keyRef)
[Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];
uint8_t *plainBuffer;
uint8_t *cipherBuffer;
uint8_t *decryptedBuffer;
const char inputString[] = "1234";
int len = strlen(inputString);
// TODO: this is a hack since i know inputString length will be less than BUFFER_SIZE
if (len > BUFFER_SIZE) len = BUFFER_SIZE-1;
plainBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));
cipherBuffer = (uint8_t *)calloc(CIPHER_BUFFER_SIZE, sizeof(uint8_t));
decryptedBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));
strncpy( (char *)plainBuffer, inputString, len);
size_t plainBufferSize = strlen((char *)plainBuffer);
size_t cipherBufferSize = CIPHER_BUFFER_SIZE;
NSLog(@"SecKeyGetBlockSize() public = %lu", SecKeyGetBlockSize(keyRef));
// Error handling
// Encrypt using the public.
OSStatus status = noErr;
status = SecKeyEncrypt(keyRef,
PADDING,
plainBuffer,
plainBufferSize,
&cipherBuffer[0],
&cipherBufferSize
);
NSLog(@"encryption result code: %ld (size: %lu)", status, cipherBufferSize);
return [[[NSString stringWithFormat:@"%s",cipherBuffer] dataUsingEncoding:NSUTF8StringEncoding] base64EncodedString];
}
For testing purposes and simplicity for the moment I am trying to encrypt only a input with a length of 4 bytes. This should be small enough to fit one block. The public key import and the encrypting process seems to work, however I always receive a much longer output compared to the android method.
The only difference I encountered so far is the fact, that SecKeyGetBlockSize returns 16 and in java cipher.blocksize returns 5. I think the other 11 bytes are reserved for the pkcs1 padding, but how can force the same behaviour in ios/objc?