为何要加密
为什么要加密，顾名思义，如果你不想让别人轻而易举的就拿到你的账号以及登录密码，如果你不想让别人获取你的敏感的数据(利益、聊天等数据),and so on; 不对数据进行加密，那就像你只穿个裤头，在到处跑，随时都可能走光；加密的重要性，我不多说，自己悟吧;
iOS 开发中经常用到的几种加密方式：MD5、Base64、RSA、AES
一般来说最常用的就是MD5和Base64：
- MD5主要应用于普通请求、返回数据，进行数据完整性校验
- Base64 主要用于防止数据明文传输
- AES 一般用于登录加密
- RSA 经常用于重要数据 以及敏感数据的加密
MD5
- (NSString *) stringFromMD5 {
if(self == nil || [self length] == 0) { return nil;
} const char *value = [self UTF8String]; unsigned char outputBuffer[CC_MD5_DIGEST_LENGTH];
CC_MD5(value, strlen(value), outputBuffer);
NSMutableString *outputString = [[NSMutableString alloc] initWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
for(NSInteger count = 0; count < CC_MD5_DIGEST_LENGTH; count++){ [outputString appendFormat:@"%02x",outputBuffer[count]];
} return outputString;
}
导入头文件：#import <CommonCrypto/CommonDigest.h>
该方法为NSString的分类方法
Base64
static const char _base64EncodingTable[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
};
+ (NSString *) encodeBase64WithString: (NSString *) strData {
NSData *objData = [strData dataUsingEncoding:NSUTF8StringEncoding];
const unsigned char * objRawData = [objData bytes];
char * objPointer; char * strResult; // Get the Raw Data length and ensure we actually have data
int intLength = [objData length]; if (intLength == 0) return nil; // Setup the String-based Result placeholder and pointer within that placeholder
strResult = (char *)calloc(((intLength + 2) / 3) * 4, sizeof(char)); objPointer = strResult; // Iterate through everything
while (intLength > 2) { // keep going until we have less than 24 bits *objPointer++ = _base64EncodingTable[objRawData[0] >> 2]; *objPointer++ = _base64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)]; *objPointer++ = _base64EncodingTable[((objRawData[1] & 0x0f) << 2) + (objRawData[2] >> 6)]; *objPointer++ = _base64EncodingTable[objRawData[2] & 0x3f]; // we just handled 3 octets (24 bits) of data
objRawData += 3; intLength -= 3; } // now deal with the tail end of things if (intLength != 0) { *objPointer++ = _base64EncodingTable[objRawData[0] >> 2]; if (intLength > 1) { *objPointer++ = _base64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)]; *objPointer++ = _base64EncodingTable[(objRawData[1] & 0x0f) << 2]; *objPointer++ = '='; } else { *objPointer++ = _base64EncodingTable[(objRawData[0] & 0x03) << 4]; *objPointer++ = '='; *objPointer++ = '='; } } // Terminate the string-based result
*objPointer = '\0'; NSString *rstStr = [NSString stringWithCString:strResult encoding:NSASCIIStringEncoding]; free(objPointer); return rstStr; }
+ (NSData *)decodeBase64WithString:(NSString *)strBase64 {
const char *objPointer = [strBase64 cStringUsingEncoding:NSASCIIStringEncoding];
size_t intLength = strlen(objPointer);
int intCurrent;
int i = 0, j = 0, k;
unsigned char *objResult = calloc(intLength, sizeof(unsigned char));
// Run through the whole string, converting as we go
while ( ((intCurrent = *objPointer++) != '\0') && (intLength-- > 0) ) {
if (intCurrent == '=') {
if (*objPointer != '=' && ((i % 4) == 1)) {// || (intLength > 0)) {
// the padding character is invalid at this point -- so this entire string is invalid
free(objResult);
return nil;
}
continue;
}
intCurrent = _base64DecodingTable[intCurrent];
if (intCurrent == -1) {
// we're at a whitespace -- simply skip over
continue;
} else if (intCurrent == -2) {
// we're at an invalid character
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++;
}
// mop things up if we ended on a boundary
k = j;
if (intCurrent == '=') {
switch (i % 4) {
case 1:
// Invalid state
free(objResult);
return nil;
case 2:
k++;
// flow through
case 3:
objResult[k] = 0;
}
}
// Cleanup and setup the return NSData
NSData * objData = [[NSData alloc] initWithBytes:objResult length:j];
free(objResult);
return objData;
}
RSA
RSA: 比较复杂，这有一篇博客可以参考iOS下的RSA加密算法
AES
对于AES 这也有一个不错的博客AES加密算法