哈希值用作表示大量数据的固定大小的唯一值。数据的少量更改会在哈希值中产生不可预知的大量更改。
sha256 的作用就是防止数据被篡改
上代码
#import <CommonCrypto/CommonDigest.h>
#import <CommonCrypto/CommonHMAC.h>
- (NSString *)hmac:(NSString *)plaintext withKey:(NSString *)key
{
const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [plaintext cStringUsingEncoding:NSASCIIStringEncoding];
unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
NSData *HMACData = [NSData dataWithBytes:cHMAC length:sizeof(cHMAC)];
const unsigned char *buffer = (const unsigned char *)[HMACData bytes];
NSMutableString *HMAC = [NSMutableString stringWithCapacity:HMACData.length * 2];
for (int i = 0; i < HMACData.length; ++i){
[HMAC appendFormat:@"%02x", buffer[i]];
}
return HMAC;
}
