IOS下Base64加密

　　Base64加密是常用的加密算法，在IOS的Des加密算法中已经使用到了Base64算法，还是单独整理出来吧。

Base64.h文件

//
//  Base64.h
//  Copyright (c) 2014年 grant. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Based64 : NSObject

//Base64加密
+ (NSString *) encodeBase64WithString:(NSString *)strData;
+ (NSString *) encodeBase64WithData:(NSData *)objData;

//Based64解密
+ (NSData *) decodeBase64WithString:(NSString *)strBase64;

@end

Base64.m文件

//
//  Base64.m
//  Copyright (c) 2014年 grant. All rights reserved.
//

#import "Base64.h"

static const char _bas64EncodingTable[64] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const short _base64DecodingTable[256] = {
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -1, -1, -2, -1, -1, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -1, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, 62, -2, -2, -2, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -2, -2, -2, -2, -2, -2,
    -2,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -2, -2, -2, -2, -2,
    -2, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2
};

@implementation Base64

+ (NSString *)encodeBase64WithString:(NSString *)strData {
    return [Based64 encodeBase64WithData:[strData dataUsingEncoding:NSUTF8StringEncoding]];
}

+ (NSString *)encodeBase64WithData:(NSData *)objData {
    const unsigned char * objRawData = [objData bytes];
    char * objPointer;
    char * strResult;

    int intLength = [objData length];
    if (intLength == 0) return nil;

    strResult = (char *)calloc(((intLength + 2) / 3) * 4, sizeof(char));
    objPointer = strResult;

    while(intLength > 2) {
        *objPointer++ = _bas64EncodingTable[objRawData[0] >> 2];
        *objPointer++ = _bas64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)];
        *objPointer++ = _bas64EncodingTable[((objRawData[1] & 0x0f) << 2) + (objRawData[2] >> 6)];
        *objPointer++ = _bas64EncodingTable[objRawData[2] & 0x3f];

        objRawData += 3;
        intLength -= 3;
    }

    if (intLength != 0) {
        *objPointer++ = _bas64EncodingTable[objRawData[0] >> 2];
        if (intLength > 1) {
            *objPointer++ = _bas64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)];
            *objPointer++ = _bas64EncodingTable[(objRawData[1] & 0x0f) << 2];
            *objPointer++ = ‘=‘;
        } else {
            *objPointer++ = _bas64EncodingTable[(objRawData[0] & 0x03) << 4];
            *objPointer++ = ‘=‘;
            *objPointer++ = ‘=‘;
        }
    }

    *objPointer = ‘\0‘;

    return[NSString stringWithCString:strResult encoding:NSASCIIStringEncoding];
}

+ (NSData *)decodeBase64WithString:(NSString *)strBase64 {
    const char* objPointer = [strBase64 cStringUsingEncoding:NSASCIIStringEncoding];
    int intLength = strlen(objPointer);
    int intCurrent;
    int i = 0, j = 0, k;

    unsigned char * objResult;
    objResult = calloc(intLength, sizeof(char));

    while ( ((intCurrent = *objPointer++) != ‘\0‘) && (intLength-- > 0) ) {
        if (intCurrent == ‘=‘) {
            if (*objPointer != ‘=‘ && ((i % 4) == 1)) {// || (intLength > 0)) {
                free(objResult);
                return nil;
            }
            continue;
        }

        intCurrent = _base64DecodingTable[intCurrent];
        if (intCurrent == -1) {
            continue;
        } else if (intCurrent == -2) {
            free(objResult);
            return nil;
        }

        switch (i % 4) {
            case 0:
                objResult[j] = intCurrent << 2;
                break;

            case 1:
                objResult[j++] |= intCurrent >> 4;
                objResult[j] = (intCurrent & 0x0f) << 4;
                break;

            case 2:
                objResult[j++] |= intCurrent >>2;
                objResult[j] = (intCurrent & 0x03) << 6;
                break;

            case 3:
                objResult[j++] |= intCurrent;
                break;
        }
        i++;
    }

    k = j;
    if (intCurrent == ‘=‘) {
        switch (i % 4) {
            case 1:
                free(objResult);
                return nil;
            case 2:
                k++;
            case 3:
                objResult[k] = 0;
        }
    }

    NSData * objData = [[NSData alloc] initWithBytes:objResult length:j] ;
    free(objResult);
    return objData;
}

@end