iOS-AES對稱加密

阿新 • • 發佈：2018-11-01

實驗要求

程式語言不限制
明文“學號+姓名+專業+學院”
實現對明文的加密，輸出密文
對密文實現解密，輸出明文
不能是DES加密演算法
報告中說明該語言提供的加密函式都有哪些，具體的使用方法並分析優缺點

程式碼

#import "ViewController.h"
#import "AES.h"
#import "NSString+AES.h"


@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //原文資訊
    NSString *plainText = @"3180807001+黃振鋒+電腦科學與技術+網路空間安全學院";
    //祕鑰
    NSString *key = @"HuangZhenFeng";
    NSLog(@"純加密:%@",[plainText AES256_Encrypt:key]);
    NSLog(@"純解密:%@",[[plainText AES256_Encrypt:key] AES256_Decrypt:key]);

    //原文轉碼資料NSData
    NSData *plainData = [plainText dataUsingEncoding:NSUTF8StringEncoding];
    //用祕鑰加密
    NSData *cipher = [plainData AES256EncryptWithKey:key];
    //得到密文
    NSLog(@"密文:%@",[cipher base64EncodedStringWithOptions:0]);
    
    //用祕鑰解密
    NSData *cipher1 = [cipher AES256DecryptWithKey:key];
    //得到明文
    NSString *plainText1 = [[NSString alloc] initWithData:cipher1 encoding:NSUTF8StringEncoding];
    NSLog(@"明文:%@",plainText1);
}
#import "AES.h"
#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonCryptor.h>

static char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

@implementation NSData (AES)

- (NSData *)AES256EncryptWithKey:(NSString *)key {
    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
    bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
    
    // fetch key data
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    
    NSUInteger dataLength = [self length];
    
    //See the doc: For block ciphers, the output size will always be less than or
    //equal to the input size plus the size of one block.
    //That's why we need to add the size of one block here
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    
    free(buffer); //free the buffer;
    return nil;
}

- (NSData *)AES256DecryptWithKey:(NSString *)key {
    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
    bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
    
    // fetch key data
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    
    NSUInteger dataLength = [self length];
    
    //See the doc: For block ciphers, the output size will always be less than or
    //equal to the input size plus the size of one block.
    //That's why we need to add the size of one block here
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesDecrypted);
    
    if (cryptStatus == kCCSuccess) {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }
    
    free(buffer); //free the buffer;
    return nil;
}


- (NSString *)newStringInBase64FromData            //追加64編碼
{
    NSMutableString *dest = [[NSMutableString alloc] initWithString:@""];
    unsigned char * working = (unsigned char *)[self bytes];
    int srcLen = [self length];
    for (int i=0; i<srcLen; i += 3) {
        for (int nib=0; nib<4; nib++) {
            int byt = (nib == 0)?0:nib-1;
            int ix = (nib+1)*2;
            if (i+byt >= srcLen) break;
            unsigned char curr = ((working[i+byt] << (8-ix)) & 0x3F);
            if (i+nib < srcLen) curr |= ((working[i+nib] >> ix) & 0x3F);
            [dest appendFormat:@"%c", base64[curr]];
        }
    }
    return dest;
}

+ (NSString*)base64encode:(NSString*)str
{
    if ([str length] == 0)
        return @"";
    const char *source = [str UTF8String];
    int strlength  = strlen(source);
    char *characters = malloc(((strlength + 2) / 3) * 4);
    if (characters == NULL)
        return nil;
    NSUInteger length = 0;
    NSUInteger i = 0;
    while (i < strlength) {
        char buffer[3] = {0,0,0};
        short bufferLength = 0;
        while (bufferLength < 3 && i < strlength)
            buffer[bufferLength++] = source[i++];
        characters[length++] = base64[(buffer[0] & 0xFC) >> 2];
        characters[length++] = base64[((buffer[0] & 0x03) << 4) | ((buffer[1] & 0xF0) >> 4)];
        if (bufferLength > 1)
            characters[length++] = base64[((buffer[1] & 0x0F) << 2) | ((buffer[2] & 0xC0) >> 6)];
        else characters[length++] = '=';
        if (bufferLength > 2)
            characters[length++] = base64[buffer[2] & 0x3F];
        else characters[length++] = '=';
    }
    NSString *g = [[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES];
    return g;
}
#import "NSData+AES.h"

@implementation NSData (AES)

//加密
- (NSData *) AES256_Encrypt:(NSString *)key{
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    NSUInteger dataLength = [self length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [self bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    free(buffer);
    return nil;
}
//解密
- (NSData *) AES256_Decrypt:(NSString *)key{
    
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    NSUInteger dataLength = [self length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [self bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
        
    }
    free(buffer);
    return nil;
}
#import "NSString+AES.h"

@implementation NSString (AES)

//加密
- (NSString *) AES256_Encrypt:(NSString *)key{
    const char *cstr = [self cStringUsingEncoding:NSUTF8StringEncoding];
    NSData *data = [NSData dataWithBytes:cstr length:self.length];
    //對資料進行加密
    NSData *result = [data AES256_Encrypt:key];
    
    //轉換為2進位制字串
    if (result && result.length > 0) {
        
        Byte *datas = (Byte*)[result bytes];
        NSMutableString *output = [NSMutableString stringWithCapacity:result.length * 2];
        for(int i = 0; i < result.length; i++){
            [output appendFormat:@"%02x", datas[i]];
        }
        return output;
    }
    return nil;
}
//解密
- (NSString *) AES256_Decrypt:(NSString *)key{
    //轉換為2進位制Data
    NSMutableData *data = [NSMutableData dataWithCapacity:self.length / 2];
    unsigned char whole_byte;
    char byte_chars[3] = {'\0','\0','\0'};
    int i;
    for (i=0; i < [self length] / 2; i++) {
        byte_chars[0] = [self characterAtIndex:i*2];
        byte_chars[1] = [self characterAtIndex:i*2+1];
        whole_byte = strtol(byte_chars, NULL, 16);
        [data appendBytes:&whole_byte length:1];
    }
    //對資料進行解密
    NSData* result = [data AES256_Decrypt:key];
    if (result && result.length > 0) {
        return [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding];
    }
    return nil;}

在這裡插入圖片描述

總結

常見的對稱加密演算法有DES、3DES、AES。
本次實驗使用對稱加密演算法是AES，AES是高階加密，也是目前使用最多的對稱加密演算法，目前美國國家安全域性使用AES加密，蘋果的鑰匙串訪問就是使用AES加密。對稱加密的優點是演算法公開，計算量小，加密速度快，加密效率高。對稱加密的缺點是雙方使用相同的鑰匙，安全性得不到保證。使用對稱加密需要注意的是祕鑰的保密工作需要非常重視，並且祕鑰要求定期更換。
實驗中，我先使用純AES演算法加解密，然後我再使用AES+Base64演算法加解密。我使用的是Objective-C語言進行程式設計，我先使用AES演算法純加密的時候，我發現加密方法目前不支援中文加解密，所以解密出來的東西為空，但是是數字或者英文的時候，可以加解密。後來我使用AES+Base64演算法的時候，可以對中文進行正常的加解密。AES+Base64實際上是在純AES演算法上再對加密內容進行Base64加密，得到一串不含空格的英文、數字、符號的組合字串。其中，純AES演算法加解密函式分別是：- (NSData *) AES256_Encrypt:(NSString *)key;，- (NSData *) AES256_Decrypt:(NSString *)key;。AES+Base64演算法加解密函式為：- (NSData *)AES256EncryptWithKey:(NSString *)key; - (NSData *)AES256DecryptWithKey:(NSString *)key; - (NSString *)newStringInBase64FromData;。其中key是自定義的祕鑰，我的祕鑰設定為“HuangZhenFeng”，明文不需要用引數傳遞進入，因為Objective-C支援在函式裡面使用“self”來提取誰呼叫這個函式，所以就能取到原文資訊。

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