BASE64轉換，內含:IOS自帶DES加解密

最近項目需要保密，於是乎小小研究了一下，發現蘋果自帶密碼庫，不錯！

//引入IOS自帶密碼庫
#import <CommonCrypto/CommonCryptor.h>

IOS支持的加解密算法如下

enum {
    kCCAlgorithmAES128 = 0,
    kCCAlgorithmDES,        
    kCCAlgorithm3DES,       
    kCCAlgorithmCAST,       
    kCCAlgorithmRC4,
    kCCAlgorithmRC2,   
    kCCAlgorithmBlowfish    
};
typedef uint32_t CCAlgorithm;

其中前4個位DES/ADES，後兩個位RSA，DES/ADES加解密使用相同的key，RSA使用公鑰加密、私鑰解密。

我就介紹下，把文本轉換成爲BASE64格式字符串後，再進行DES加密、解密，把BASE64格式字符串轉換爲文本的過程。

爲了調用起來方便，我建立了轉換宏

#define __BASE64( text )        [CommonFunc base64StringFromText:text]
#define __TEXT( base64 )        [CommonFunc textFromBase64String:base64]

文本與BASE64格式字符串轉換實現如下:

/******************************************************************************
 函數名稱 : + (NSData *)dataWithBase64EncodedString:(NSString *)string
 函數描述 : base64格式字符串轉換爲文本數據
 輸入參數 : (NSString *)string
 輸出參數 : N/A
 返回參數 : (NSData *)
 備註信息 :
 ******************************************************************************/
+ (NSData *)dataWithBase64EncodedString:(NSString *)string
{
    if (string == nil)
        [NSException raise:NSInvalidArgumentException format:nil];
    if ([string length] == 0)
        return [NSData data];
    
    static char *decodingTable = NULL;
    if (decodingTable == NULL)
    {
        decodingTable = malloc(256);
        if (decodingTable == NULL)
            return nil;
        memset(decodingTable, CHAR_MAX, 256);
        NSUInteger i;
        for (i = 0; i < 64; i++)
            decodingTable[(short)encodingTable[i]] = i;
    }
    
    const char *characters = [string cStringUsingEncoding:NSASCIIStringEncoding];
    if (characters == NULL)     //  Not an ASCII string!
        return nil;
    char *bytes = malloc((([string length] + 3) / 4) * 3);
    if (bytes == NULL)
        return nil;
    NSUInteger length = 0;
    
    NSUInteger i = 0;
    while (YES)
    {
        char buffer[4];
        short bufferLength;
        for (bufferLength = 0; bufferLength < 4; i++)
        {
            if (characters[i] == '\0')
                break;
            if (isspace(characters[i]) || characters[i] == '=')
                continue;
            buffer[bufferLength] = decodingTable[(short)characters[i]];
            if (buffer[bufferLength++] == CHAR_MAX)      //  Illegal character!
            {
                free(bytes);
                return nil;
            }
        }
        
        if (bufferLength == 0)
            break;
        if (bufferLength == 1)      //  At least two characters are needed to produce one byte!
        {
            free(bytes);
            return nil;
        }
        
        //  Decode the characters in the buffer to bytes.
        bytes[length++] = (buffer[0] << 2) | (buffer[1] >> 4);
        if (bufferLength > 2)
            bytes[length++] = (buffer[1] << 4) | (buffer[2] >> 2);
        if (bufferLength > 3)
            bytes[length++] = (buffer[2] << 6) | buffer[3];
    }
    
    bytes = realloc(bytes, length);
    return [NSData dataWithBytesNoCopy:bytes length:length];
}

/******************************************************************************
 函數名稱 : + (NSString *)base64EncodedStringFrom:(NSData *)data
 函數描述 : 文本數據轉換爲base64格式字符串
 輸入參數 : (NSData *)data
 輸出參數 : N/A
 返回參數 : (NSString *)
 備註信息 : 
 ******************************************************************************/
+ (NSString *)base64EncodedStringFrom:(NSData *)data
{
    if ([data length] == 0)
        return @"";
    
    char *characters = malloc((([data length] + 2) / 3) * 4);
    if (characters == NULL)
        return nil;
    NSUInteger length = 0;
    
    NSUInteger i = 0;
    while (i < [data length])
    {
        char buffer[3] = {0,0,0};
        short bufferLength = 0;
        while (bufferLength < 3 && i < [data length])
            buffer[bufferLength++] = ((char *)[data bytes])[i++];
        
        //  Encode the bytes in the buffer to four characters, including padding "=" characters if necessary.
        characters[length++] = encodingTable[(buffer[0] & 0xFC) >> 2];
        characters[length++] = encodingTable[((buffer[0] & 0x03) << 4) | ((buffer[1] & 0xF0) >> 4)];
        if (bufferLength > 1)
            characters[length++] = encodingTable[((buffer[1] & 0x0F) << 2) | ((buffer[2] & 0xC0) >> 6)];
        else characters[length++] = '=';
        if (bufferLength > 2)
            characters[length++] = encodingTable[buffer[2] & 0x3F];
        else characters[length++] = '=';
    }
    
    return [[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES];
}

DES加密、解密實現如下:

/******************************************************************************
 函數名稱 : + (NSData *)DESEncrypt:(NSData *)data WithKey:(NSString *)key
 函數描述 : 文本數據進行DES加密
 輸入參數 : (NSData *)data    
          (NSString *)key
 輸出參數 : N/A
 返回參數 : (NSData *)
 備註信息 : 此函數不可用於過長文本
 ******************************************************************************/
+ (NSData *)DESEncrypt:(NSData *)data WithKey:(NSString *)key
{
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    
    NSUInteger dataLength = [data length];
    
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmDES,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeDES,
                                          NULL,
                                          [data bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    
    free(buffer);
    return nil;
}

/******************************************************************************
 函數名稱 : + (NSData *)DESEncrypt:(NSData *)data WithKey:(NSString *)key
 函數描述 : 文本數據進行DES解密
 輸入參數 : (NSData *)data
          (NSString *)key
 輸出參數 : N/A
 返回參數 : (NSData *)
 備註信息 : 此函數不可用於過長文本
 ******************************************************************************/
+ (NSData *)DESDecrypt:(NSData *)data WithKey:(NSString *)key
{
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    
    NSUInteger dataLength = [data length];
    
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmDES,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeDES,
                                          NULL,
                                          [data bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);
    
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }
    
    free(buffer);
    return nil;
}

然後把兩者結合起來使用，我認爲更加安全，於是我就這樣做了:

+ (NSString *)base64StringFromText:(NSString *)text
{
    if (text && ![text isEqualToString:LocalStr_None]) {
        //取項目的bundleIdentifier作爲KEY
        NSString *key = [[NSBundle mainBundle] bundleIdentifier];
        NSData *data = [text dataUsingEncoding:NSUTF8StringEncoding];
        //IOS 自帶DES加密 Begin
        data = [self DESEncrypt:data WithKey:key];
        //IOS 自帶DES加密 End
        return [self base64EncodedStringFrom:data];
    }
    else {
        return LocalStr_None;
    }
}

+ (NSString *)textFromBase64String:(NSString *)base64
{
    if (base64 && ![base64 isEqualToString:LocalStr_None]) {
        //取項目的bundleIdentifier作爲KEY
        NSString *key = [[NSBundle mainBundle] bundleIdentifier];
        NSData *data = [self dataWithBase64EncodedString:base64];
        //IOS 自帶DES解密 Begin
        data = [self DESDecrypt:data WithKey:key];
        //IOS 自帶DES加密 End
        return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    }
    else {
        return LocalStr_None;
    }
}