在线校验网站：https://the-x.cn/cryptography/Aes.aspx

AES有ECB和CBC模式，目前采用的是AES128-ECB-NOPadding模式

直接上代码：

#import <UIKit/UIKit.h>
#import <CommonCrypto/CommonDigest.h>
#import <CommonCrypto/CommonCryptor.h>

/**
 * AES工具类
 */
NS_ASSUME_NONNULL_BEGIN

@interface AESUtil : NSObject
/**
 * AES加密
 */
+ (NSString *)AES128Encrypt:(NSString *)data key:(NSString *)key;

/**
 * AES解密
 */
+ (NSString *)AES128Decrypt:(NSString *)data key:(NSString *)key;

@end

NS_ASSUME_NONNULL_END

#import <Foundation/Foundation.h>
#import "AESUtil.h"

@interface AESUtil()

@end
 
@implementation AESUtil

//解密
+ (NSString *)AES128Decrypt:(NSString *)str key:(NSString *)keyStr{
    NSData *data = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];
    NSData *key = [keyStr utf8Data];
    
    char keyPtr[kCCKeySizeAES128+1];
    bzero(keyPtr, sizeof(keyPtr));
    //[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    [key getBytes:keyPtr length:kCCKeySizeAES128+1];
    NSUInteger dataLength = [data length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [data bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);
    if (cryptStatus == kCCSuccess) {
        NSData *resultData = [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
        NSString *utfStr = [[NSString alloc] initWithData:resultData encoding:NSUTF8StringEncoding];
        return utfStr;
    }
    free(buffer);
    return nil;
}

//加密
+ (NSString *)AES128Encrypt:(NSString *)str key:(NSString *)keyStr {
    NSData *data = [str utf8Data];
    NSData *key = [keyStr utf8Data];
    
    char keyPtr[kCCKeySizeAES128+1];
    bzero(keyPtr, sizeof(keyPtr));
    //[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    [key getBytes:keyPtr length:kCCKeySizeAES128+1];
    NSUInteger dataLength = [data length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [data bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        NSData *resultData = [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
        return [resultData base64EncodedStringWithOptions:0];
    }
    free(buffer);
    return nil;
}

@end

- (NSData *)utf8Data{
    return [self dataUsingEncoding:NSUTF8StringEncoding];
}

256位的参考：
https://dandelioncloud.cn/article/details/1534494198132928514

//
// LanAES.m
// AESSample
//
// Created by Things on 2017/8/17.
// Copyright © 2017年 Xanthuim. All rights reserved.
//
#import "AESUtil.h"
@implementation AESUtil
//解密
+ (NSData *) AES256_Decrypt:(NSData *)data withKey:(NSData *)key{
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    //[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    [key getBytes:keyPtr length:kCCKeySizeAES128+1];
    NSUInteger dataLength = [data length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [data bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }
    free(buffer);
    return nil;
}
//加密
+ (NSData *) AES256_Encrypt:(NSData *)data withKey:(NSData *)key {
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    //[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    [key getBytes:keyPtr length:kCCKeySizeAES128+1];
    NSUInteger dataLength = [data length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [data bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    free(buffer);
    return nil;
}
@end