Encryption using public key - iphone

Question

My code:
SecKeyRef oPublicKey = [self getPublicKeyRef];
SecKeyRef oPrivateKey = [self getPrivateKeyRef];
CFDictionaryRef myDictionary;
CFTypeRef keys[2];
CFTypeRef values[2];
// Initialize dictionary of key params
keys[0] = kSecAttrKeyType;
values[0] = kSecAttrKeyTypeRSA;
keys[1] = kSecAttrKeySizeInBits;
int iByteSize = 1024;
values[1] = CFNumberCreate( NULL, kCFNumberIntType, &iByteSize );
myDictionary = CFDictionaryCreate( NULL, keys, values, sizeof(keys) / sizeof(keys[0]), NULL, NULL );
// Generate keys
OSStatus status = SecKeyGeneratePair( myDictionary, &oPublicKey, &oPrivateKey );
if ( status != 0 )
NSLog( #"SecKeyGeneratePair failed" );
// Encrypt some data
uint8_t* pPlainText = (uint8_t*)"6921";
uint8_t aCipherText[1024];
size_t iCipherLength = 1024;
status = SecKeyEncrypt( oPublicKey, kSecPaddingPKCS1, pPlainText, strlen( (char*)pPlainText ) + 1, &aCipherText[0], &iCipherLength );
if ( status != 0 )
NSLog( #"SecKeyEncrypt failed" );
NSMutableData *data12=[[NSMutableData alloc] init];
[data12 appendBytes:aCipherText length:strlen( (char*)aCipherText ) + 1];
NSString *string1 = [[NSString alloc]initWithData:data12 encoding:NSASCIIStringEncoding];
NSLog(#"Encrypted Text:::%#",string1);
// Decrypt the data
uint8_t aPlainText[1024];
size_t iPlainLength = 1024;
status = SecKeyDecrypt( oPrivateKey, kSecPaddingPKCS1, &aCipherText[0], iCipherLength, &aPlainText[0], &iPlainLength );
if ( status != 0 )
NSLog( #"SecKeyDecrypt failed" );
NSLog(#"FINAL decrypted text: %s", aPlainText);
I am using this code for encryption but we are getting output like:
N$) : )¥=wÞ¢#4+ ’MO, œÝՑ#2< xՁ™‘Hþ a  f¦šU;f£Æì ø¤VØ´ÿ ÷ påcx ¨¢¯Ô)Õ#k Ë«: çÑ5
õ°7\ہ‰z~“9GX>M¼êe뿆w¥ro¬ ›gP4s2µ)9; p
But how to get NSString format ?Is there any wrong step in my code?

Answer 1

Always pad your plain text. PKCS #1 is the standard padding for RSA encryption.
Also, be aware that with RSA public key encryption, you can only encrypt/decrypt data up to the size of the key (minus a few overhead bytes).
Public key encryption is typically used only to encrypt a key (and hash), which is then used for symmetric encryption (and verification) of the actual payload.