AesGcm

ObjC implementation of Galois/Counter Mode (GCM) with Advanced Encryption System (AES).

Installation

AesGcm is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "AesGcm"

Usage

#import <AesGcm/IAGAesGcm.h>
#import <CommonCrypto/CommonCrypto.h>

// Define an Encryption Key
u_char keyBytes[kCCKeySizeAES128] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10};
NSData *key = [NSData dataWithBytes:keyBytes length:sizeof(keyBytes)];

// Define an Initialization Vector
// GCM recommends a IV size of 96 bits (12 bytes), but you are free to use other sizes
u_char ivBytes[12] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C};
NSData *iv = [NSData dataWithBytes:ivBytes length:sizeof(ivBytes)];

// Define an Additional Authenticated Data
NSData *aad = [@"AdditionalAuthenticatedData" dataUsingEncoding:NSUTF8StringEncoding];

// Now, we are ready to encrypt some plain data
NSData *expectedPlainData = [@"PlainData" dataUsingEncoding:NSUTF8StringEncoding];

// The returned ciphered data is a simple class with 2 properties: the actual encrypted data and the authentication tag.
// The authentication tag can have multiple sizes and it is up to you to set one, in this case the size is 128 bits
// (16 bytes)
IAGCipheredData *cipheredData = [IAGAesGcm cipheredDataByAuthenticatedEncryptingPlainData:expectedPlainData
                                                          withAdditionalAuthenticatedData:aad
                                                                  authenticationTagLength:IAGAuthenticationTagLength128
                                                                     initializationVector:iv
                                                                                      key:key
                                                                                    error:nil];

// And now, de-cypher the encrypted data to see if the returned plain data is as expected
NSData *plainData = [IAGAesGcm plainDataByAuthenticatedDecryptingCipheredData:cipheredData
                                              withAdditionalAuthenticatedData:aad
                                                         initializationVector:iv
                                                                          key:key
                                                                        error:nil];

XCTAssertEqualObjects(expectedPlainData, plainData);

Acknowledgements

This implementation is based on the following documents:

• Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC
• The Galois/Counter Mode of Operation (GCM)

License

AesGcm is available under the MIT license. See the LICENSE file for more info.