Skip32（加密 32 位）

库代码片段

skip32

适用于 PostgreSQL

任何版本

用

PL/pgSQL

依赖于

无

skip32 使用 10 字节（80 位）bytea 类型密钥加密或解密单个 int4（32 位）值。

它可用于生成看起来随机的唯一值序列，或模糊 SERIAL 主键而不丢失其唯一性属性。

Skip32 基于 Skipjack 分组密码。

通过 PGXN 上的 cryptint 扩展 也提供了 C 实现。它的运行速度比这里提出的 plpgsql 版本快得多，但需要超级用户编译和安装。

警告：使用像 Skipjack 这样短加密密钥的算法被认为对于拥有当今计算能力和密码分析知识的足够有动机的攻击者来说太容易破解了。不要将此用于真正的加密。

/*
   Encrypts an integer (4 bytes) with the Skip32 block cipher
   based on Skipjack.
   Arguments:  
      - int4 value to encrypt/decrypt
      - bytea encryption key, 10 bytes long
      - direction: true to encrypt, false to decrypt
   
   Encrypt usage:
     select skip32(1234, bytea '\xC0ffeeFaceC0ffeeFeed', true);
   Decrypt usage:
     select skip32(783287961, bytea '\xC0ffeeFaceC0ffeeFeed', false);

   As each value encrypts into another unique value (given an encryption
   key), this may be used to obfuscate an int4 primary key without loosing
   the unicity property.

   plpgsql implementation by Daniel Vérité.
   Based on C code from:
     SKIP32 -- 32 bit block cipher based on SKIPJACK.
     Written by Greg Rose, QUALCOMM Australia, 1999/04/27.
   See also:
     http://search.cpan.org/~esh/Crypt-Skip32-0.17/
*/
create or replace function skip32(val int4, cr_key bytea, encrypt bool) returns int4
as $$
declare
  kstep int;
  k int;
  wl int4;
  wr int4;
  g1 int4;
  g2 int4;
  g3 int4;
  g4 int4;
  g5 int4;
  g6 int4;
  ftable bytea:='\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';
begin
  if (octet_length(cr_key)!=10) then
    raise exception 'The encryption key must be exactly 10 bytes long.';
  end if;

  if (encrypt) then
    kstep := 1;
    k := 0;
  else
    kstep := -1;
    k := 23;
  end if;

  wl := (val & -65536) >> 16;
  wr := val & 65535;

  for i in 0..11 loop
    g1 := (wl>>8) & 255;
    g2 := wl & 255;
    g3 := get_byte(ftable, g2 # get_byte(cr_key, (4*k)%10)) # g1;
    g4 := get_byte(ftable, g3 # get_byte(cr_key, (4*k+1)%10)) # g2;
    g5 := get_byte(ftable, g4 # get_byte(cr_key, (4*k+2)%10)) # g3;
    g6 := get_byte(ftable, g5 # get_byte(cr_key, (4*k+3)%10)) # g4;
    wr := wr # (((g5<<8) + g6) # k);
    k := k + kstep;
 
    g1 := (wr>>8) & 255;
    g2 := wr & 255;
    g3 := get_byte(ftable, g2 # get_byte(cr_key, (4*k)%10)) # g1;
    g4 := get_byte(ftable, g3 # get_byte(cr_key, (4*k+1)%10)) # g2;
    g5 := get_byte(ftable, g4 # get_byte(cr_key, (4*k+2)%10)) # g3;
    g6 := get_byte(ftable, g5 # get_byte(cr_key, (4*k+3)%10)) # g4;
    wl := wl # (((g5<<8) + g6) # k);
    k := k + kstep;
  end loop;

  return (wr << 16) | (wl & 65535);

end
$$ immutable strict language plpgsql;

示例输出

SELECT
  x,
  encx AS encrypted,
  skip32(encx, 'nooneknows'::bytea,false) AS decrypted
FROM (SELECT x, skip32(x, 'nooneknows'::bytea, true) AS encx
      FROM generate_series(-10,10) AS x
   ) AS s;

  x  |  encrypted  | decrypted 
-----+-------------+-----------
 -10 |  -487745093 |       -10
  -9 | -2112342827 |        -9
  -8 |  1303049886 |        -8
  -7 | -1084841580 |        -7
  -6 |   560956799 |        -6
  -5 |    82237967 |        -5
  -4 |   425659720 |        -4
  -3 | -2105383591 |        -3
  -2 | -1511018704 |        -2
  -1 | -1020536589 |        -1
   0 |  1500550465 |         0
   1 |  1203450477 |         1
   2 |  1404417409 |         2
   3 |  -495049695 |         3
   4 | -1940533399 |         4
   5 |  -121441692 |         5
   6 |  1957824249 |         6
   7 | -1677320563 |         7
   8 |    21505071 |         8
   9 | -1867910739 |         9
  10 | -1277220617 |        10

(21 rows)