我的 SHA256 OCaml 实现是否正常？

Question

我是一名 OCaml 程序员新手，我认为尝试实现一个非常棘手的算法会让自己陷入困境。 我对所有大大小小的批评持开放态度，无论是风格方面的、安全方面的还是性能方面的。

我已经意识到的一个批评是该算法需要将整个消息放入内存中（而 SHA256 的参考实现一次可以处理一个块）。

我特别关心是否有任何递归函数不是尾递归的。

我已经测试了代码，它确实在 x86_64 Linux 上生成了正确的消息摘要。

预先感谢您的考虑。

编辑：

如果您没有什么发现，请不要在这里花太多时间。 我正在寻找明显损坏的行为，而不是重写。

let as_bytes bits =
  match (bits mod 8) with
    | 0 -> (bits / 8)
    | _ -> failwith "as_bytes: bits must be multiple of 8"
let as_bits bytes = bytes * 8
let k = [|
    0x428a2f98l; 0x71374491l; 0xb5c0fbcfl; 0xe9b5dba5l;
    0x3956c25bl; 0x59f111f1l; 0x923f82a4l; 0xab1c5ed5l;
    0xd807aa98l; 0x12835b01l; 0x243185bel; 0x550c7dc3l;
    0x72be5d74l; 0x80deb1fel; 0x9bdc06a7l; 0xc19bf174l;
    0xe49b69c1l; 0xefbe4786l; 0x0fc19dc6l; 0x240ca1ccl;
    0x2de92c6fl; 0x4a7484aal; 0x5cb0a9dcl; 0x76f988dal;
    0x983e5152l; 0xa831c66dl; 0xb00327c8l; 0xbf597fc7l;
    0xc6e00bf3l; 0xd5a79147l; 0x06ca6351l; 0x14292967l;
    0x27b70a85l; 0x2e1b2138l; 0x4d2c6dfcl; 0x53380d13l;
    0x650a7354l; 0x766a0abbl; 0x81c2c92el; 0x92722c85l;
    0xa2bfe8a1l; 0xa81a664bl; 0xc24b8b70l; 0xc76c51a3l;
    0xd192e819l; 0xd6990624l; 0xf40e3585l; 0x106aa070l;
    0x19a4c116l; 0x1e376c08l; 0x2748774cl; 0x34b0bcb5l;
    0x391c0cb3l; 0x4ed8aa4al; 0x5b9cca4fl; 0x682e6ff3l;
    0x748f82eel; 0x78a5636fl; 0x84c87814l; 0x8cc70208l;
    0x90befffal; 0xa4506cebl; 0xbef9a3f7l; 0xc67178f2l
  |]
  let hash s =
    let add_int32 x y = Int32.add x y in

    let left_int32 x n = Int32.shift_left x n in
    let right_int32 x n = Int32.shift_right_logical x n in
    let or_int32 x y = Int32.logor x y in
    let xor_int32 x y = Int32.logxor x y in
    let and_int32 x y = Int32.logand x y in
    let not_int32 x = Int32.lognot x in

    let rotate x n = (or_int32 (right_int32 x n) (left_int32 x (32 - n))) in
    let shift x n = right_int32 x n in
    let ch x y z = xor_int32 (and_int32 x y) (and_int32 (not_int32 x) z) in
    let maj x y z = (xor_int32 (and_int32 x y) (xor_int32 (and_int32 x z) (and_int32 y z))) in
    let sum0 x = (xor_int32 (rotate x  2) (xor_int32 (rotate x 13) (rotate x 22))) in
    let sum1 x = (xor_int32 (rotate x  6) (xor_int32 (rotate x 11) (rotate x 25))) in
    let rh00 x = (xor_int32 (rotate x  7) (xor_int32 (rotate x 18) (shift  x  3))) in
    let rh01 x = (xor_int32 (rotate x 17) (xor_int32 (rotate x 19) (shift  x 10))) in

    let as_bytes bits =
      match (bits mod 8) with
        | 0 -> (bits / 8)
        | _ -> failwith "as_bytes: bits must be multiple of 8"
    in
    let as_bits bytes = bytes * 8 in
    let sha = [|
      0x6a09e667l;
      0xbb67ae85l;
      0x3c6ef372l;
      0xa54ff53al;
      0x510e527fl;
      0x9b05688cl;
      0x1f83d9abl;
      0x5be0cd19l
    |]
    in
    let message = Buffer.create (as_bytes 512) in (* smallest possible buffer is at least 512 bits *)
      begin
        Buffer.add_string message s;
        let original_length = as_bits (Buffer.length message) in 
        Buffer.add_char message '\x80'; (* append '1' bit *)
          let pad_start = as_bits (Buffer.length message) in
          let pad_blocks = if (original_length mod 512) < 448 then 1 else 2 in
          let message_length = ((original_length / 512) + pad_blocks) * 512 in
            begin (* appending k bits of 0 (where message_length-64 is our k) *)
              for i = as_bytes pad_start to (as_bytes (message_length - (as_bytes  64)))-8 do
                Buffer.add_char message '\x00'
              done;
              Buffer.add_buffer message (Bin.pack64 (Int64.of_int original_length))
            end
      end;
      let rec process_block i blocks =
        let array_of_block i = 
          let boff = i*(as_bytes 512) in
          let to_int32 x = (Int32.of_int (int_of_char x)) in
          let w = Array.make (as_bytes 512) 0l in
            begin
              for t = 0 to 15 do
                w.(t) <- (or_int32 (left_int32 (to_int32 (Buffer.nth message (boff + (t*4  )))) 24)
                         (or_int32 (left_int32 (to_int32 (Buffer.nth message (boff + (t*4+1)))) 16)
                         (or_int32 (left_int32 (to_int32 (Buffer.nth message (boff + (t*4+2))))  8)
                                               (to_int32 (Buffer.nth message (boff + (t*4+3))))   )));
              done;
              for t = 16 to 63 do
                w.(t) <- add_int32 (add_int32 (rh01 w.(t-2)) w.(t-7)) (add_int32 (rh00 w.(t-15)) w.(t-16))
              done;
              w
            end
        in
          if i = blocks then 
            let sha256 = Buffer.create (as_bytes 256) in
            let rec pack_sha256 i =
              match i with
                | 8 -> Buffer.contents sha256
                | _ ->
                    begin
                      Buffer.add_buffer sha256 (Bin.pack32 sha.(i));
                      pack_sha256 (i+1)
                    end
            in pack_sha256 0
          else
            begin
              let w = array_of_block i in
              let tem = [| 0l; 0l |] in
                begin
                  let a = ref sha.(0) in 
                  let b = ref sha.(1) in
                  let c = ref sha.(2) in
                  let d = ref sha.(3) in 
                  let e = ref sha.(4) in
                  let f = ref sha.(5) in
                  let g = ref sha.(6) in
                  let h = ref sha.(7) in
                    for t = 0 to 63 do
                      begin
                        tem.(0) <- add_int32 (add_int32 !h (sum1 !e)) (add_int32 (ch !e !f !g) (add_int32 k.(t) w.(t)));
                        tem.(1) <- add_int32 (sum0 !a) (maj !a !b !c);
                        h := !g;
                        g := !f;
                        f := !e;
                        e := add_int32 !d tem.(0);
                        d := !c;
                        c := !b;
                        b := !a;
                        a := add_int32 tem.(0) tem.(1);
                       end
                    done;
                    sha.(0) <- add_int32 sha.(0) !a;
                    sha.(1) <- add_int32 sha.(1) !b;
                    sha.(2) <- add_int32 sha.(2) !c;
                    sha.(3) <- add_int32 sha.(3) !d;
                    sha.(4) <- add_int32 sha.(4) !e;
                    sha.(5) <- add_int32 sha.(5) !f;
                    sha.(6) <- add_int32 sha.(6) !g;
                    sha.(7) <- add_int32 sha.(7) !h;

                    (* good faith attempt to clear memory *)
                    for i = 0 to 63 do w.(t) <- 0 done;
                    tem.(0) <- 0; tem.(1) <- 0;
                    a := 0; b := 0; c := 0; d := 0; e := 0; f := 0; g := 0; h := 0;
                end;
            process_block (i+1) blocks
          end
  in process_block 0 ((Buffer.length message) / (as_bytes 512))

  let hexdigits s =
    let rec hexdigits_inner hx i =
      match i with
        | 32 -> hx
        | _ -> hexdigits_inner (hx ^ (Printf.sprintf "%02x" (int_of_char s.[i]))) (i+1)
    in
      hexdigits_inner "" 0

在单独的文件中定义的 pack 函数如下：

let pack64 x = 
  let b = Buffer.create 8 in 
    for i = 0 to 7 do
      let shft = (7-i)*8 in
        Buffer.add_char b (char_of_int (Int64.to_int (Int64.logand (Int64.shift_right x shft) 0xFFL)));
    done;
    b

let pack x n = 
  if (n mod 8) = 0 then
    let n' = n/8 in
    let b = Buffer.create n' in 
      for i = 0 to n'-1 do
        let shft = ((n'-1)-i)*8 in
          Buffer.add_char b (char_of_int (Int32.to_int (Int32.logand (Int32.shift_right x shft) 0xFFl)));
      done;
      b
  else
    raise (Invalid_argument ("pack: " ^ (string_of_int n) ^ " is not a multiple of 8"))

let pack32 x = pack x 32
let pack16 x = pack x 16
let pack8 x = pack x 8

Answer 1

您应该做的第一件事是从标准中获取测试向量，并验证您的实现是否生成完全相同的结果。 如果没有，那就坏了。

如果您有一个“已知的健全”实现（openssl 命令可能有一个），您还可以生成其他测试向量。

最后，使用逐渐变大的文件运行一些性能测试，并与已知的快速实现进行比较（openssl 应该相当快）。 如果失败（耗尽所有内存或速度太慢），您必须对其进行修复。

如果它通过了所有这些测试，那么它应该已经足够好了。 哈希算法不应该有太多安全问题（除非您正在对敏感数据进行哈希处理，否则您必须非常小心地覆盖您使用的所有内存）。