Mathematica 中的 HMAC（基于哈希的消息验证码，又名数据签名）答案

【问题标题】：HMAC (hash-based message authentication code, aka data signing) in MathematicaMathematica 中的 HMAC（基于哈希的消息验证码，又名数据签名）
【发布时间】：2009-12-05 07:17:07
【问题描述】：

似乎在所有语言中都有 HMAC 的实现。（见下文。）而且算法非常简单：

http://en.wikipedia.org/wiki/HMAC

有人在 Mathematica 中实现过吗？

这里是指向其他语言实现的指针：

【问题讨论】：

标签： authentication hash code-signing wolfram-mathematica

【解决方案1】：

这是我的实现：

首先是一些实用功能：

(* Pad the string s with x on the right/left so it has length n. *)
strpadr[s_, n_, x_] := StringJoin@PadRight[Characters[s], n, x]
strpadl[s_, n_, x_] := StringJoin@PadLeft[Characters[s], n, x]

(* hex representation; optionally pad to length n with zeros *)
hex[x_, n_:Null]:= If[n===Null, Identity, strpadl[#,n,"0"]&]@IntegerString[x,16]

(* parse hex representation (return an integer) *)
unhex[x_] := FromDigits[x, 16]

(* Concatenate all the arguments as strings (if they're not already). *)
cat = StringJoin @@ (ToString /@ {##}) &;

(* Takes a string like "xy" and returns the hex representation (also a string, 
   twice as long) of the bytes (ascii codes). *)
tobytes[s_] := cat @@ (hex[#, 2] & /@ ToCharacterCode[s])

(* Takes a length n string like "0a10" and returns a length n/2 string where in 
   this example the first character is whatever has ascii code 10 ("a" in hex) 
   and the second is whatever has ascii code 16 ("10" in hex). *)
frombytes[hs_] := FromCharacterCode[unhex /@ cat@@@Partition[Characters[hs], 2]]

(* Bitwise-xor of two integers given in hex. *)
hexbitxor[a_String, b_String] := hex@BitXor[unhex@a, unhex@b]

(* Repeat the string s, n times. *)
strrpt[s_, n_] := cat @@ ConstantArray[s, n]

(* Byte length of a hex string is half the string length. *)
bytelen[s_] := Ceiling[StringLength[s]/2]

在 Mathematica 中实现基本的哈希函数并非易事。看到这个问题： Cryptographic hash (sha1 or md5) of data given as a string in Mathematica.

(* FileHash is the only way to hash data given as a string in Mma. *)
hash[s_String, h_:"SHA"] := Module[{stream = StringToStream[s], result},
  result = FileHash[stream, h];
  Close[stream];
  hex@result];
sha1[s_] := hash[s]
md5[s_] := hash[s, "MD5"]

最后是hmac函数：

(* Return the hmac digest using hash function h for string s with key k. *)
hmac[s_, k_, h_:sha1] := Module[{b, key, ipad, opad},
  b = 64; (* block size for both md5 and sha1 *)
  key = tobytes[k];
  key = If[bytelen[key] > b, h[frombytes@key], key];
  key = strpadr[key, 2 b, "0"];
  ipad = hexbitxor[strrpt["36", b], key];
  opad = hexbitxor[strrpt["5c", b], key];
  h[frombytes[opad <> h[frombytes[ipad <> tobytes@s]]]]]

我确认这符合RFC 2104 中提供的所有示例。例如：

hmac["what do ya want for nothing?", "Jefe", md5]

"750c783e6ab0b503eaa86e310a5db738"

【讨论】：