Objective-C AES/GCM/NoPadding crypto

AES_GCM.m

// pod 'AesGcm'
#import <AesGcm/IAGAesGcm.h>

// replace with your own key, base64 encoding
static NSString * const AES_GCM_KEY = @"MTIzNDU2Nzg5MGFiY2RlZg==";

- (NSString *)encryptString:(NSString *)text {
    NSData *key = [[NSData alloc] initWithBase64EncodedString:AES_GCM_KEY options:NSDataBase64DecodingIgnoreUnknownCharacters];
    NSData *iv = [self randomKeyDataGeneratorWithNumberBits:96];

    NSData *aad = [NSData data];

    NSData *plainData = [text dataUsingEncoding:NSUTF8StringEncoding];

    // when
    IAGCipheredData *cipheredData = [IAGAesGcm cipheredDataByAuthenticatedEncryptingPlainData:plainData
                                                              withAdditionalAuthenticatedData:aad
                                                                      authenticationTagLength:IAGAuthenticationTagLength128
                                                                         initializationVector:iv
                                                                                          key:key
                                                                                        error:nil];

    // then
    NSData *cipheredBuffer = [NSData dataWithBytes:cipheredData.cipheredBuffer
                                            length:cipheredData.cipheredBufferLength];
    NSData *extraBuffer = [NSData dataWithBytes:cipheredData.authenticationTag
                                         length:cipheredData.authenticationTagLength];
    NSMutableData *fullBuffer = [[NSMutableData alloc] initWithData:iv];
    [fullBuffer appendData:cipheredBuffer];
    [fullBuffer appendData:extraBuffer];

    NSString *ciphertext = [fullBuffer base64EncodedStringWithOptions:0];
    return ciphertext;
}

- (NSString *)decryptString:(NSString *)encryptedString {
    // given
    NSData *key = [[NSData alloc] initWithBase64EncodedString:AES_GCM_KEY options:NSDataBase64DecodingIgnoreUnknownCharacters];
    NSData *aad = [NSData data];
    NSData *encryptedData = [[NSData alloc] initWithBase64EncodedString:encryptedString options:NSDataBase64DecodingIgnoreUnknownCharacters];
    NSData *iv = [encryptedData subdataWithRange:NSMakeRange(0, 12)];

    NSData *ciphertext = [encryptedData subdataWithRange:NSMakeRange(12, encryptedData.length - 12 - 16)];
    NSData *authTag = [encryptedData subdataWithRange:NSMakeRange(encryptedData.length - 16, 16)];
    IAGCipheredData *cipheredData = [[IAGCipheredData alloc] initWithCipheredBuffer:ciphertext.bytes
                                                               cipheredBufferLength:ciphertext.length
                                                                  authenticationTag:authTag.bytes
                                                            authenticationTagLength:authTag.length];

    // when
    NSData *plainData = [IAGAesGcm plainDataByAuthenticatedDecryptingCipheredData:cipheredData
                                                  withAdditionalAuthenticatedData:aad
                                                             initializationVector:iv
                                                                              key:key
                                                                            error:nil];

    // then
    NSString *plainText = [[NSString alloc] initWithData:plainData encoding:NSUTF8StringEncoding];
    return plainText;
}

/*!
 * @brief Generates NSData from a randomly generated byte array with a specific number of bits
 * @param numberOfBits the number of bits the generated data must have
 * @return the randomly generated NSData
 */
- (NSData *)randomKeyDataGeneratorWithNumberBits:(int)numberOfBits {
    int numberOfBytes = numberOfBits/8;
    uint8_t randomBytes[numberOfBytes];
    int result = SecRandomCopyBytes(kSecRandomDefault, numberOfBytes, randomBytes);
    if(result == 0) {
        return [NSData dataWithBytes:randomBytes length:numberOfBytes];
    } else {
        return nil;
    }
}

when string is so large, the lib will crash