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copied!<p>Your code is leaking the first allocation of output.</p> <p>Besides that it looks mostly ok.</p> <p>This is a complete end-to-end implementation using a SHA256 hash of the user's passphrase (in this case 'Salamander') and base64'ing the output. There is a PHP test implementation in the source that reconstructs the key then trims the PKCS7 padding before giving final output. A decryptor in Ruby follows, the PKCS7 padding removal happens automatically by the OpenSSL::Cipher.</p> <p>Here you go:</p> <pre><code>// Crypto categories for iOS #import <CommonCrypto/CommonCryptor.h> #import <CommonCrypto/CommonDigest.h> @interface NSData( Crypto ) - (NSData *) aesEncryptedDataWithKey:(NSData *) key; - (NSString *) base64Encoding; @end @interface NSString( Crypto ) - (NSData *) sha256; @end // -------- @implementation NSData( Crypto ) - (NSData *) aesEncryptedDataWithKey:(NSData *) key { unsigned char *buffer = nil; size_t bufferSize; CCCryptorStatus err; NSUInteger i, keyLength, plainTextLength; // make sure there's data to encrypt err = ( plainTextLength = [self length] ) == 0; // pass the user's passphrase through SHA256 to obtain 32 bytes // of key data. Use all 32 bytes for an AES256 key or just the // first 16 for AES128. if ( ! err ) { switch ( ( keyLength = [key length] ) ) { case kCCKeySizeAES128: case kCCKeySizeAES256: break; // invalid key size default: err = 1; break; } } // create an output buffer with room for pad bytes if ( ! err ) { bufferSize = kCCBlockSizeAES128 + plainTextLength + kCCBlockSizeAES128; // iv + cipher + padding err = ! ( buffer = (unsigned char *) malloc( bufferSize ) ); } // encrypt the data if ( ! err ) { srandomdev(); // generate a random iv and prepend it to the output buffer. the // decryptor needs to be aware of this. for ( i = 0; i < kCCBlockSizeAES128; ++i ) buffer[ i ] = random() & 0xff; err = CCCrypt( kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding, [key bytes], keyLength, buffer, [self bytes], plainTextLength, buffer + kCCBlockSizeAES128, bufferSize - kCCBlockSizeAES128, &bufferSize ); } if ( err ) { if ( buffer ) free( buffer ); return nil; } // dataWithBytesNoCopy takes ownership of buffer and will free() it // when the NSData object that owns it is released. return [NSData dataWithBytesNoCopy: buffer length: bufferSize + kCCBlockSizeAES128]; } - (NSString *) base64Encoding { char *encoded, *r; const char eTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; unsigned i, l, n, t; UInt8 *p, pad = '='; NSString *result; p = (UInt8 *) [self bytes]; if ( ! p || ( l = [self length] ) == 0 ) return @""; r = encoded = malloc( 4 * ( ( n = l / 3 ) + ( l % 3 ? 1 : 0 ) ) + 1 ); if ( ! encoded ) return nil; for ( i = 0; i < n; ++i ) { t = *p++ << 16; t |= *p++ << 8; t |= *p++; *r++ = eTable[ t >> 18 ]; *r++ = eTable[ t >> 12 & 0x3f ]; *r++ = eTable[ t >> 6 & 0x3f ]; *r++ = eTable[ t & 0x3f ]; } if ( ( i = n * 3 ) < l ) { t = *p++ << 16; *r++ = eTable[ t >> 18 ]; if ( ++i < l ) { t |= *p++ << 8; *r++ = eTable[ t >> 12 & 0x3f ]; *r++ = eTable[ t >> 6 & 0x3f ]; } else { *r++ = eTable[ t >> 12 & 0x3f ]; *r++ = pad; } *r++ = pad; } *r = 0; result = [NSString stringWithUTF8String: encoded]; free( encoded ); return result; } @end @implementation NSString( Crypto ) - (NSData *) sha256 { unsigned char *buffer; if ( ! ( buffer = (unsigned char *) malloc( CC_SHA256_DIGEST_LENGTH ) ) ) return nil; CC_SHA256( [self UTF8String], [self lengthOfBytesUsingEncoding: NSUTF8StringEncoding], buffer ); return [NSData dataWithBytesNoCopy: buffer length: CC_SHA256_DIGEST_LENGTH]; } @end // ----------------- @implementation AppDelegate - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { NSData *plain = [@"This is a test of the emergency broadcast system." dataUsingEncoding: NSUTF8StringEncoding]; NSData *key = [NSData dataWithBytes: [[@"Salamander" sha256] bytes] length: kCCKeySizeAES128]; NSData *cipher = [plain aesEncryptedDataWithKey: key]; NSString *base64 = [cipher base64Encoding]; NSLog( @"cipher: %@", base64 ); // stuff the base64'ed cipher into decrypt.php: // http://localhost/~par/decrypt.php?cipher=<base64_output> /* <?php header( "content-type: text/plain" ); if ( ! ( $cipher = $_GET[ 'cipher' ] ) ) { echo "no cipher parameter found"; return; } echo "cipher: $cipher\n"; $cipher = base64_decode( $cipher ); $iv = substr( $cipher, 0, 16 ); $cipher = substr( $cipher, 16 ); // use the full key (all 32 bytes) for aes256 $key = substr( hash( "sha256", "Salamander", true ), 0, 16 ); $plainText = mcrypt_decrypt( MCRYPT_RIJNDAEL_128, $key, $cipher, MCRYPT_MODE_CBC, $iv ); $plainTextLength = strlen( $plainText ); // strip pkcs7 padding $padding = ord( $plainText[ $plainTextLength - 1 ] ); $plainText = substr( $plainText, 0, -$padding ); printf( "plaintext: %s\n", $plainText ); ?> */ return YES; } @end </code></pre> <p>Decryption of the output of the above in Ruby:</p> <pre><code>require 'base64' require 'openssl' def decrypt( cipherBase64 ) cipher = Base64.decode64( cipherBase64 ) aes = OpenSSL::Cipher::Cipher.new( "aes-128-cbc" ).decrypt aes.iv = cipher.slice( 0, 16 ) # don't slice the SHA256 output for AES256 aes.key = ( Digest::SHA256.digest( 'Salamander' ) ).slice( 0, 16 ) cipher = cipher.slice( 16..-1 ) return aes.update( cipher ) + aes.final end text = '3o4ARWOxwmLEPgq3SJ3A2ws7sUSxMvWSKbbs+oABsOcywk+9qPBoDjhLAfAW/n28pbnsT2w5QMSye6pz3Lz8xmg5BYL8HdfKwbS9EpTbaUc=' print decrypt( text ) + "\n" </code></pre>

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