Encrypt data with RSA public key not giving expected results - ios

Question

I'm trying to encrypt data with an RSA public key using openssl.
I have the Java implementation of what I need to do in Objective-C.
Here's what I have so far:
- (RSA *)rsaFromExponent:(NSString *)exponent modulus:(NSString *)modulus
{
RSA *rsa_pub = RSA_new();
const char *N = [modulus UTF8String];
const char *E = [exponent UTF8String];
if (!BN_hex2bn(&rsa_pub->n, N))
{
// TODO
}
printf("N: %s\n", N);
printf("n: %s\n", BN_bn2dec(rsa_pub->n));
if (!BN_hex2bn(&rsa_pub->e, E))
{
// TODO
}
printf("E: %s\n", E);
printf("e: %s\n", BN_bn2dec(rsa_pub->e));
return rsa_pub;
}
- (NSString *)cleanString:(NSString *)input
{
NSString *output = input;
output = [output stringByReplacingOccurrencesOfString:#"<" withString:#""];
output = [output stringByReplacingOccurrencesOfString:#">" withString:#""];
output = [output stringByReplacingOccurrencesOfString:#" " withString:#""];
return output;
}
// main code
NSString *exponentB64 = #"AQAB";
NSString *modulusB64 = #"AKDbnFpblq7LHfWDfGTR48B34MKaHQosMwVu8cCc6fH2pZ8Ypx/OgzG6VJlKHXeELtlo5tddBSJpwnkEQdvkkmwuOpCkacTTLon6EHqX4WwFW+waqHxmj419SxiDDlo9tsbg7vfFIMpKyGzq1zvTAN3TroW+MxogZfZD3/N6dNTzvBoXe/Ca1e/zVwYXKbiegLMjNwsruz/WvuMiNKTK4U3GEmb0gIODd1shAH10ube8Nrz/e1u9kr25VQ+7kZAFjnkPTp2AvNGYHQt35m1TRMQhTylVwTZqFkHC/jMt7WxuS8q7ftjM828wa1fEWTgWYrdkzmqZSK5CHBYSys/N1Ws=";
// 1. decode base64 (http://projectswithlove.com/projects/NSData_Base64.zip)
NSData *exponent = [NSData dataFromBase64String:exponentB64];
NSData *modulus = [NSData dataFromBase64String:modulusB64];
NSString *exponentHex = [self cleanString:[exponent description]];
NSString *modulusHex = [self cleanString:[modulus description]];
// 2. create RSA public key
RSA *rsa_pub = [self rsaFromExponent:exponentHex modulus:modulusHex];
NSString *user = #"TEST";
// 3. encode base 64
NSData *userData = [user dataUsingEncoding:NSASCIIStringEncoding];
NSString *userB64String = [userData base64EncodedString];
// 4. encrypt
const unsigned char *from = (const unsigned char *)[userB64String cStringUsingEncoding:NSASCIIStringEncoding];
int flen = strlen((const char *)from);
unsigned char *to = (unsigned char *) malloc(RSA_size(rsa_pub));
int padding = RSA_PKCS1_PADDING;
int result = RSA_public_encrypt(flen, from, to, rsa_pub, padding);
if (-1 == result)
{
NSLog(#"WAT?");
}
else
{
NSLog(#"from: %s", from); // echo VEVTVA==
NSLog(#"to: %s", to); // echo something strange with characters like: ~™Ÿû—...
}
// 5. encode base 64
NSString *cipherString = [NSString stringWithCString:(const char *)to
encoding:NSASCIIStringEncoding];
NSData *cipherData = [cipherString dataUsingEncoding:NSASCIIStringEncoding];
NSString *cipherDataB64 = [cipherData base64EncodedString];
NSLog(#"user encrypted b64: %#", cipherDataB64); // echo null :-(
In Java, I have no problem to base64 encode the encrypted data.
I'm sure I'm doing something wrong but I don't know where because it's not something I do everyday.
Or if you know another way to do this with iOS frameworks like Security.framework.
Thanks in advance.

Answer 1

Someone else helped me figure it out. I don't know why but I was assuming that the output buffer from RSA_public_encrypt function would be an ascii string. Though it's just bytes as the documentation says too. The char * type often leads me to think it's gonna store a string (it's so wrong I think it's the last time I make this kind of error).
So from step 5:
// 5. encode base 64
NSData *cipherData = [NSData dataWithBytes:(const void *)to length:result];
NSString *cipherDataB64 = [cipherData base64EncodedString];
NSLog(#"user encrypted b64: %#", cipherDataB64); // now echo the expected value