ios项目开发（天气预报项目）:hmacsha1 例子

- (NSString *)hmacsha1:(NSString *)text key:(NSString *)secret {
NSData *secretData = [secret dataUsingEncoding:NSUTF8StringEncoding];
NSData *clearTextData = [text dataUsingEncoding:NSUTF8StringEncoding];
unsigned char result[20];
CCHmac(kCCHmacAlgSHA1, [secretData bytes], [secretData length], [clearTextData bytes], [clearTextData length], result);

char base64Result[32];
size_t theResultLength = 32;
Base64EncodeData(result, 20, base64Result, &theResultLength);
NSData *theData = [NSData dataWithBytes:base64Result length:theResultLength];

NSString *base64EncodedResult = [[NSString alloc] initWithData:theData encoding:NSASCIIStringEncoding];

return base64EncodedResult;
}