简介
Blowfish 是一种具有 Feistel 结构的加密算法，block_size 为 64，rounds为 16。 它使用给定的 key 生成若干 sub keys，表现为一个长度为 18 的 32 位P数组(P-array), 和 4 个长度为 256，每一项都是一个 32 位数的 substitution boxes(S-boxes)。
加密步骤
- 使用 key 初始化
P-array和S-boxes - 将明文分割为若干个 64bit 的 block，不足时需要补 0
- 将 64-bit 的 block 分割为两个 32bit 的部分，进行 16 轮循环，最后再和 P17,P18 分别异或(
XOR)并交换 - 组合 blocks
下面详细介绍每个步骤的过程
初始化 sub keys
初始化 P-array
初始的P是圆周率 π 的小数部分，每 32 位作为 P 的一项，如：
- P[0] = "243f6a88"
- P[1] = "85a308d3" ...
- P[17] = "8979fb1b"
然后对于每个 P[i]将其与给定的 key 的每 32 位依次进行按位异或(XOR)操作，如果 key 不够长，则将 key 循环拼接。
- P[0] = P[0] XOR key 第 1 个 32 位
- P[1] = P[1] XOR key 第 2 个 32 位 ...
- P[17] = P[17] XOR key 的第 18 个 32 位 （如 key 到达结尾，则从头开始取，直到取够 32 位）
初始化 S-boxes
blowfish 需要 4 个 256 项（S[i][0] - S[i][255]），每项 32 位的 substitution boxes. 初始的 S-boxes 值需要从初始化完 P-array 后的圆周率 π 的位置继续，每 32 位取一项，直到将 4 个 S-boxes 填满。
利用 blowfish 计算新的 P-array 和 S-boxes
首先使用 blowfish 算法本身加密 0x0000000000000000 这个 64 位的 0，此时使用刚刚初始化的 P 和 S。
具体的加密算法实现将在下文详细介绍，加密函数的签名为
INPUT:plain_text, P, S OUTPUT: cipher_text
在加密完成后会得到 64 位的 block，将 P[0]替换为结果的前 32 位，将 P[1]替换为结果的后 32 位。然后再次使用 blowfish 加密上一轮的加密结果，和上一轮类似，替换 P[2]和 P[3]。依次进行替换直至将 P 全部替换后，再依次替换 S-boxes 中的每项。如某次加密的 64 位前 32 位替换 S[0][0]，后 32 位替换 S[0][1]...直到替换完 S[3][254]和 S[3][255]。
至此 sub keys 的初始化就完成了。初始化 sub key 总计需要进行 （18 + 256 * 4）/ 2 = 521 次加密运算。
这种进行多轮运算生成 sub-key 的结构，在 key 不变时，加密只需要进行一次运算，而 key 变动时则需要进行 521 次运算，重新计算 sub keys。由于一般应用中 key 并不会经常变动，因此这种结构能够有效的减慢 key 被爆破的速度而不降低应用时加密的速度。
加密算法
每次加密需要先进行 16 轮 Feistel 结构的循环，每轮循环中首先将 64 位的 block 分为 32 位的两半 xL 和 xR, 然后进行一系列运算，伪代码如下：
For i = 1 to 16:
xL = xL XOR Pi
xR = F(xL) XOR xR
Swap xL and xR
Next i
Swap xL and xR (Undo the last swap.)
xR = xR XOR P17
xL = xL XOR P18
Recombine xL and xR
其中的 F 函数，需要将每个输入的 32 位的 xL 分割为 4 个 8 位的部分 a, b, c, d，
F(xL) = ((((S[0][a] + S[1][b]) % 2^32) XOR S[2][c]) + S[3][d]) % 2^32
简单的说就是 S[0][a]加模 S[1][b]异或XORS[2][c] 再加模 S[3][d]
解密
解密的过程和加密完全相同，只不过使用 P 的顺序需要反过来，前 16 轮循环使用 P[17], P[16], P[15], P[14]... 最后异或交换时使用 P[1], P[0]
实现
定义变量
P = [
"243f6a88",
"85a308d3",
"13198a2e",
"03707344",
"a4093822",
"299f31d0",
"082efa98",
"ec4e6c89",
"452821e6",
"38d01377",
"be5466cf",
"34e90c6c",
"c0ac29b7",
"c97c50dd",
"3f84d5b5",
"b5470917",
"9216d5d9",
"8979fb1b",
]
P = [int(s, 16) for s in P]
S = [
["d1310ba6", "98dfb5ac", "2ffd72db", "d01adfb7", "b8e1afed",
"6a267e96", "ba7c9045", "f12c7f99", "24a19947", "b3916cf7",
"0801f2e2", "858efc16", "636920d8", "71574e69", "a458fea3",
"f4933d7e", "0d95748f", "728eb658", "718bcd58", "82154aee",
"7b54a41d", "c25a59b5", "9c30d539", "2af26013", "c5d1b023",
"286085f0", "ca417918", "b8db38ef", "8e79dcb0", "603a180e",
"6c9e0e8b", "b01e8a3e", "d71577c1", "bd314b27", "78af2fda",
"55605c60", "e65525f3", "aa55ab94", "57489862", "63e81440",
"55ca396a", "2aab10b6", "b4cc5c34", "1141e8ce", "a15486af",
"7c72e993", "b3ee1411", "636fbc2a", "2ba9c55d", "741831f6",
"ce5c3e16", "9b87931e", "afd6ba33", "6c24cf5c", "7a325381",
"28958677", "3b8f4898", "6b4bb9af", "c4bfe81b", "66282193",
"61d809cc", "fb21a991", "487cac60", "5dec8032", "ef845d5d",
"e98575b1", "dc262302", "eb651b88", "23893e81", "d396acc5",
"0f6d6ff3", "83f44239", "2e0b4482", "a4842004", "69c8f04a",
"9e1f9b5e", "21c66842", "f6e96c9a", "670c9c61", "abd388f0",
"6a51a0d2", "d8542f68", "960fa728", "ab5133a3", "6eef0b6c",
"137a3be4", "ba3bf050", "7efb2a98", "a1f1651d", "39af0176",
"66ca593e", "82430e88", "8cee8619", "456f9fb4", "7d84a5c3",
"3b8b5ebe", "e06f75d8", "85c12073", "401a449f", "56c16aa6",
"4ed3aa62", "363f7706", "1bfedf72", "429b023d", "37d0d724",
"d00a1248", "db0fead3", "49f1c09b", "075372c9", "80991b7b",
"25d479d8", "f6e8def7", "e3fe501a", "b6794c3b", "976ce0bd",
"04c006ba", "c1a94fb6", "409f60c4", "5e5c9ec2", "196a2463",
"68fb6faf", "3e6c53b5", "1339b2eb", "3b52ec6f", "6dfc511f",
"9b30952c", "cc814544", "af5ebd09", "bee3d004", "de334afd",
"660f2807", "192e4bb3", "c0cba857", "45c8740f", "d20b5f39",
"b9d3fbdb", "5579c0bd", "1a60320a", "d6a100c6", "402c7279",
"679f25fe", "fb1fa3cc", "8ea5e9f8", "db3222f8", "3c7516df",
"fd616b15", "2f501ec8", "ad0552ab", "323db5fa", "fd238760",
"53317b48", "3e00df82", "9e5c57bb", "ca6f8ca0", "1a87562e",
"df1769db", "d542a8f6", "287effc3", "ac6732c6", "8c4f5573",
"695b27b0", "bbca58c8", "e1ffa35d", "b8f011a0", "10fa3d98",
"fd2183b8", "4afcb56c", "2dd1d35b", "9a53e479", "b6f84565",
"d28e49bc", "4bfb9790", "e1ddf2da", "a4cb7e33", "62fb1341",
"cee4c6e8", "ef20cada", "36774c01", "d07e9efe", "2bf11fb4",
"95dbda4d", "ae909198", "eaad8e71", "6b93d5a0", "d08ed1d0",
"afc725e0", "8e3c5b2f", "8e7594b7", "8ff6e2fb", "f2122b64",
"8888b812", "900df01c", "4fad5ea0", "688fc31c", "d1cff191",
"b3a8c1ad", "2f2f2218", "be0e1777", "ea752dfe", "8b021fa1",
"e5a0cc0f", "b56f74e8", "18acf3d6", "ce89e299", "b4a84fe0",
"fd13e0b7", "7cc43b81", "d2ada8d9", "165fa266", "80957705",
"93cc7314", "211a1477", "e6ad2065", "77b5fa86", "c75442f5",
"fb9d35cf", "ebcdaf0c", "7b3e89a0", "d6411bd3", "ae1e7e49",
"00250e2d", "2071b35e", "226800bb", "57b8e0af", "2464369b",
"f009b91e", "5563911d", "59dfa6aa", "78c14389", "d95a537f",
"207d5ba2", "02e5b9c5", "83260376", "6295cfa9", "11c81968",
"4e734a41", "b3472dca", "7b14a94a", "1b510052", "9a532915",
"d60f573f", "bc9bc6e4", "2b60a476", "81e67400", "08ba6fb5",
"571be91f", "f296ec6b", "2a0dd915", "b6636521", "e7b9f9b6",
"ff34052e", "c5855664", "53b02d5d", "a99f8fa1", "08ba4799",
"6e85076a" ],
["4b7a70e9", "b5b32944", "db75092e", "c4192623", "ad6ea6b0",
"49a7df7d", "9cee60b8", "8fedb266", "ecaa8c71", "699a17ff",
"5664526c", "c2b19ee1", "193602a5", "75094c29", "a0591340",
"e4183a3e", "3f54989a", "5b429d65", "6b8fe4d6", "99f73fd6",
"a1d29c07", "efe830f5", "4d2d38e6", "f0255dc1", "4cdd2086",
"8470eb26", "6382e9c6", "021ecc5e", "09686b3f", "3ebaefc9",
"3c971814", "6b6a70a1", "687f3584", "52a0e286", "b79c5305",
"aa500737", "3e07841c", "7fdeae5c", "8e7d44ec", "5716f2b8",
"b03ada37", "f0500c0d", "f01c1f04", "0200b3ff", "ae0cf51a",
"3cb574b2", "25837a58", "dc0921bd", "d19113f9", "7ca92ff6",
"94324773", "22f54701", "3ae5e581", "37c2dadc", "c8b57634",
"9af3dda7", "a9446146", "0fd0030e", "ecc8c73e", "a4751e41",
"e238cd99", "3bea0e2f", "3280bba1", "183eb331", "4e548b38",
"4f6db908", "6f420d03", "f60a04bf", "2cb81290", "24977c79",
"5679b072", "bcaf89af", "de9a771f", "d9930810", "b38bae12",
"dccf3f2e", "5512721f", "2e6b7124", "501adde6", "9f84cd87",
"7a584718", "7408da17", "bc9f9abc", "e94b7d8c", "ec7aec3a",
"db851dfa", "63094366", "c464c3d2", "ef1c1847", "3215d908",
"dd433b37", "24c2ba16", "12a14d43", "2a65c451", "50940002",
"133ae4dd", "71dff89e", "10314e55", "81ac77d6", "5f11199b",
"043556f1", "d7a3c76b", "3c11183b", "5924a509", "f28fe6ed",
"97f1fbfa", "9ebabf2c", "1e153c6e", "86e34570", "eae96fb1",
"860e5e0a", "5a3e2ab3", "771fe71c", "4e3d06fa", "2965dcb9",
"99e71d0f", "803e89d6", "5266c825", "2e4cc978", "9c10b36a",
"c6150eba", "94e2ea78", "a5fc3c53", "1e0a2df4", "f2f74ea7",
"361d2b3d", "1939260f", "19c27960", "5223a708", "f71312b6",
"ebadfe6e", "eac31f66", "e3bc4595", "a67bc883", "b17f37d1",
"018cff28", "c332ddef", "be6c5aa5", "65582185", "68ab9802",
"eecea50f", "db2f953b", "2aef7dad", "5b6e2f84", "1521b628",
"29076170", "ecdd4775", "619f1510", "13cca830", "eb61bd96",
"0334fe1e", "aa0363cf", "b5735c90", "4c70a239", "d59e9e0b",
"cbaade14", "eecc86bc", "60622ca7", "9cab5cab", "b2f3846e",
"648b1eaf", "19bdf0ca", "a02369b9", "655abb50", "40685a32",
"3c2ab4b3", "319ee9d5", "c021b8f7", "9b540b19", "875fa099",
"95f7997e", "623d7da8", "f837889a", "97e32d77", "11ed935f",
"16681281", "0e358829", "c7e61fd6", "96dedfa1", "7858ba99",
"57f584a5", "1b227263", "9b83c3ff", "1ac24696", "cdb30aeb",
"532e3054", "8fd948e4", "6dbc3128", "58ebf2ef", "34c6ffea",
"fe28ed61", "ee7c3c73", "5d4a14d9", "e864b7e3", "42105d14",
"203e13e0", "45eee2b6", "a3aaabea", "db6c4f15", "facb4fd0",
"c742f442", "ef6abbb5", "654f3b1d", "41cd2105", "d81e799e",
"86854dc7", "e44b476a", "3d816250", "cf62a1f2", "5b8d2646",
"fc8883a0", "c1c7b6a3", "7f1524c3", "69cb7492", "47848a0b",
"5692b285", "095bbf00", "ad19489d", "1462b174", "23820e00",
"58428d2a", "0c55f5ea", "1dadf43e", "233f7061", "3372f092",
"8d937e41", "d65fecf1", "6c223bdb", "7cde3759", "cbee7460",
"4085f2a7", "ce77326e", "a6078084", "19f8509e", "e8efd855",
"61d99735", "a969a7aa", "c50c06c2", "5a04abfc", "800bcadc",
"9e447a2e", "c3453484", "fdd56705", "0e1e9ec9", "db73dbd3",
"105588cd", "675fda79", "e3674340", "c5c43465", "713e38d8",
"3d28f89e", "f16dff20", "153e21e7", "8fb03d4a", "e6e39f2b",
"db83adf7"],
["e93d5a68", "948140f7", "f64c261c", "94692934", "411520f7",
"7602d4f7", "bcf46b2e", "d4a20068", "d4082471", "3320f46a",
"43b7d4b7", "500061af", "1e39f62e", "97244546", "14214f74",
"bf8b8840", "4d95fc1d", "96b591af", "70f4ddd3", "66a02f45",
"bfbc09ec", "03bd9785", "7fac6dd0", "31cb8504", "96eb27b3",
"55fd3941", "da2547e6", "abca0a9a", "28507825", "530429f4",
"0a2c86da", "e9b66dfb", "68dc1462", "d7486900", "680ec0a4",
"27a18dee", "4f3ffea2", "e887ad8c", "b58ce006", "7af4d6b6",
"aace1e7c", "d3375fec", "ce78a399", "406b2a42", "20fe9e35",
"d9f385b9", "ee39d7ab", "3b124e8b", "1dc9faf7", "4b6d1856",
"26a36631", "eae397b2", "3a6efa74", "dd5b4332", "6841e7f7",
"ca7820fb", "fb0af54e", "d8feb397", "454056ac", "ba489527",
"55533a3a", "20838d87", "fe6ba9b7", "d096954b", "55a867bc",
"a1159a58", "cca92963", "99e1db33", "a62a4a56", "3f3125f9",
"5ef47e1c", "9029317c", "fdf8e802", "04272f70", "80bb155c",
"05282ce3", "95c11548", "e4c66d22", "48c1133f", "c70f86dc",
"07f9c9ee", "41041f0f", "404779a4", "5d886e17", "325f51eb",
"d59bc0d1", "f2bcc18f", "41113564", "257b7834", "602a9c60",
"dff8e8a3", "1f636c1b", "0e12b4c2", "02e1329e", "af664fd1",
"cad18115", "6b2395e0", "333e92e1", "3b240b62", "eebeb922",
"85b2a20e", "e6ba0d99", "de720c8c", "2da2f728", "d0127845",
"95b794fd", "647d0862", "e7ccf5f0", "5449a36f", "877d48fa",
"c39dfd27", "f33e8d1e", "0a476341", "992eff74", "3a6f6eab",
"f4f8fd37", "a812dc60", "a1ebddf8", "991be14c", "db6e6b0d",
"c67b5510", "6d672c37", "2765d43b", "dcd0e804", "f1290dc7",
"cc00ffa3", "b5390f92", "690fed0b", "667b9ffb", "cedb7d9c",
"a091cf0b", "d9155ea3", "bb132f88", "515bad24", "7b9479bf",
"763bd6eb", "37392eb3", "cc115979", "8026e297", "f42e312d",
"6842ada7", "c66a2b3b", "12754ccc", "782ef11c", "6a124237",
"b79251e7", "06a1bbe6", "4bfb6350", "1a6b1018", "11caedfa",
"3d25bdd8", "e2e1c3c9", "44421659", "0a121386", "d90cec6e",
"d5abea2a", "64af674e", "da86a85f", "bebfe988", "64e4c3fe",
"9dbc8057", "f0f7c086", "60787bf8", "6003604d", "d1fd8346",
"f6381fb0", "7745ae04", "d736fccc", "83426b33", "f01eab71",
"b0804187", "3c005e5f", "77a057be", "bde8ae24", "55464299",
"bf582e61", "4e58f48f", "f2ddfda2", "f474ef38", "8789bdc2",
"5366f9c3", "c8b38e74", "b475f255", "46fcd9b9", "7aeb2661",
"8b1ddf84", "846a0e79", "915f95e2", "466e598e", "20b45770",
"8cd55591", "c902de4c", "b90bace1", "bb8205d0", "11a86248",
"7574a99e", "b77f19b6", "e0a9dc09", "662d09a1", "c4324633",
"e85a1f02", "09f0be8c", "4a99a025", "1d6efe10", "1ab93d1d",
"0ba5a4df", "a186f20f", "2868f169", "dcb7da83", "573906fe",
"a1e2ce9b", "4fcd7f52", "50115e01", "a70683fa", "a002b5c4",
"0de6d027", "9af88c27", "773f8641", "c3604c06", "61a806b5",
"f0177a28", "c0f586e0", "006058aa", "30dc7d62", "11e69ed7",
"2338ea63", "53c2dd94", "c2c21634", "bbcbee56", "90bcb6de",
"ebfc7da1", "ce591d76", "6f05e409", "4b7c0188", "39720a3d",
"7c927c24", "86e3725f", "724d9db9", "1ac15bb4", "d39eb8fc",
"ed545578", "08fca5b5", "d83d7cd3", "4dad0fc4", "1e50ef5e",
"b161e6f8", "a28514d9", "6c51133c", "6fd5c7e7", "56e14ec4",
"362abfce", "ddc6c837", "d79a3234", "92638212", "670efa8e",
"406000e0"],
["3a39ce37", "d3faf5cf", "abc27737", "5ac52d1b", "5cb0679e",
"4fa33742", "d3822740", "99bc9bbe", "d5118e9d", "bf0f7315",
"d62d1c7e", "c700c47b", "b78c1b6b", "21a19045", "b26eb1be",
"6a366eb4", "5748ab2f", "bc946e79", "c6a376d2", "6549c2c8",
"530ff8ee", "468dde7d", "d5730a1d", "4cd04dc6", "2939bbdb",
"a9ba4650", "ac9526e8", "be5ee304", "a1fad5f0", "6a2d519a",
"63ef8ce2", "9a86ee22", "c089c2b8", "43242ef6", "a51e03aa",
"9cf2d0a4", "83c061ba", "9be96a4d", "8fe51550", "ba645bd6",
"2826a2f9", "a73a3ae1", "4ba99586", "ef5562e9", "c72fefd3",
"f752f7da", "3f046f69", "77fa0a59", "80e4a915", "87b08601",
"9b09e6ad", "3b3ee593", "e990fd5a", "9e34d797", "2cf0b7d9",
"022b8b51", "96d5ac3a", "017da67d", "d1cf3ed6", "7c7d2d28",
"1f9f25cf", "adf2b89b", "5ad6b472", "5a88f54c", "e029ac71",
"e019a5e6", "47b0acfd", "ed93fa9b", "e8d3c48d", "283b57cc",
"f8d56629", "79132e28", "785f0191", "ed756055", "f7960e44",
"e3d35e8c", "15056dd4", "88f46dba", "03a16125", "0564f0bd",
"c3eb9e15", "3c9057a2", "97271aec", "a93a072a", "1b3f6d9b",
"1e6321f5", "f59c66fb", "26dcf319", "7533d928", "b155fdf5",
"03563482", "8aba3cbb", "28517711", "c20ad9f8", "abcc5167",
"ccad925f", "4de81751", "3830dc8e", "379d5862", "9320f991",
"ea7a90c2", "fb3e7bce", "5121ce64", "774fbe32", "a8b6e37e",
"c3293d46", "48de5369", "6413e680", "a2ae0810", "dd6db224",
"69852dfd", "09072166", "b39a460a", "6445c0dd", "586cdecf",
"1c20c8ae", "5bbef7dd", "1b588d40", "ccd2017f", "6bb4e3bb",
"dda26a7e", "3a59ff45", "3e350a44", "bcb4cdd5", "72eacea8",
"fa6484bb", "8d6612ae", "bf3c6f47", "d29be463", "542f5d9e",
"aec2771b", "f64e6370", "740e0d8d", "e75b1357", "f8721671",
"af537d5d", "4040cb08", "4eb4e2cc", "34d2466a", "0115af84",
"e1b00428", "95983a1d", "06b89fb4", "ce6ea048", "6f3f3b82",
"3520ab82", "011a1d4b", "277227f8", "611560b1", "e7933fdc",
"bb3a792b", "344525bd", "a08839e1", "51ce794b", "2f32c9b7",
"a01fbac9", "e01cc87e", "bcc7d1f6", "cf0111c3", "a1e8aac7",
"1a908749", "d44fbd9a", "d0dadecb", "d50ada38", "0339c32a",
"c6913667", "8df9317c", "e0b12b4f", "f79e59b7", "43f5bb3a",
"f2d519ff", "27d9459c", "bf97222c", "15e6fc2a", "0f91fc71",
"9b941525", "fae59361", "ceb69ceb", "c2a86459", "12baa8d1",
"b6c1075e", "e3056a0c", "10d25065", "cb03a442", "e0ec6e0e",
"1698db3b", "4c98a0be", "3278e964", "9f1f9532", "e0d392df",
"d3a0342b", "8971f21e", "1b0a7441", "4ba3348c", "c5be7120",
"c37632d8", "df359f8d", "9b992f2e", "e60b6f47", "0fe3f11d",
"e54cda54", "1edad891", "ce6279cf", "cd3e7e6f", "1618b166",
"fd2c1d05", "848fd2c5", "f6fb2299", "f523f357", "a6327623",
"93a83531", "56cccd02", "acf08162", "5a75ebb5", "6e163697",
"88d273cc", "de966292", "81b949d0", "4c50901b", "71c65614",
"e6c6c7bd", "327a140a", "45e1d006", "c3f27b9a", "c9aa53fd",
"62a80f00", "bb25bfe2", "35bdd2f6", "71126905", "b2040222",
"b6cbcf7c", "cd769c2b", "53113ec0", "1640e3d3", "38abbd60",
"2547adf0", "ba38209c", "f746ce76", "77afa1c5", "20756060",
"85cbfe4e", "8ae88dd8", "7aaaf9b0", "4cf9aa7e", "1948c25c",
"02fb8a8c", "01c36ae4", "d6ebe1f9", "90d4f869", "a65cdea0",
"3f09252d", "c208e69f", "b74e6132", "ce77e25b", "578fdfe3",
"3ac372e6"]]
S = [[int(s, 16) for s in Si] for Si in S]
key = "secret"
key = bytes(key, "utf-8")
plain_text = "just Monika"
rounds = 16
初始化 sub key
def init_sub_keys():
# step1: for each P[i] xor with key
key_length = len(key)
for i in range(len(P)):
temp = 0
for j in range(4):
temp = temp << 8 | key[(j + i * 4) % key_length]
P[i] = P[i] ^ temp
# print([format(p, '032b',) for p in P])
# step2: encrypt 0x0000000000000000 with new key
# replace every 2 P[i] and S[i][j] with result of every round
block = 0x0000000000000000
for i in range(0, len(P), 2):
block = encrypt(block)
P[i], P[i + 1] = block >> 32, block & 0xFFFFFFFF
for i in range(len(S)):
for j in range(0, len(S[i]), 2):
block = encrypt(block)
S[i][j], S[i][j + 1] = block >> 32, block & 0xFFFFFFFF
加密算法
def encrypt(plain_text_block: int):
block = plain_text_block
for i in range(16):
block = round(block, P[i])
# last swap and xor
L = block >> 32 ^ P[16]
R = block & 0xFFFFFFFF ^ P[17]
return R << 32 | L
def round(block: int, Pi: int):
# divide block into 2 32-bit halves, L and R
L = block >> 32
R = block & 0xFFFFFFFF
L = L ^ Pi
R = f(L) ^ R
# swap L and R
return R << 32 | L
def f(L: int):
# divide 32-bit L half into 4 8-bit quarters
a = L >> 24
b = (L & 0x00FF0000) >> 16
c = (L & 0x0000FF00) >> 8
d = L & 0x000000FF
return ((((S[0][a] + S[1][b]) % 0x100000000) ^ S[2][c]) + S[3][d]) % 0x100000000
解密算法
def decrypt(cipher_text):
block = cipher_text
for i in range(16):
block = round(block, P[17 - i])
# last swap and xor
L = block >> 32 ^ P[1]
R = block & 0xFFFFFFFF ^ P[0]
return R << 32 | L
两个工具函数
便于在字符串和 block 之间转换
# divide string into 64bit blocks array
def str2blocks(string: str):
res = []
for i in range(0, len(string), 8):
block = 0x0000000000000000
for j in range(8):
index = -i - 1 - j
if len(string) + index >= 0:
block = ord(string[index]) << (8 * j) | block
res.insert(0, block)
return res
def block2str(block: int):
res = ""
block_bytes = block.to_bytes(8, "big")
for i in range(8):
res += chr(block_bytes[i])
return res
测试函数
def main():
init_sub_keys()
print("plain_text: ", plain_text)
# plain_text: just Monika
cipher_text = "".join(
[block2str(encrypt(block)) for block in str2blocks(plain_text)]
)
print("cipher_text: ", cipher_text)
# cipher_text: é{ÎÉPg
origin_text = "".join(
[block2str(decrypt(block)) for block in str2blocks(cipher_text)]
)
print("origin_text: ", origin_text)
# origin_text: just Monika
if __name__ == "__main__":
main()
总结
- blowfish 是一种具有 Feistel 结构的对称加密算法，起初是为了作为 DES 算法的替代。
- 在密钥不变时加密加密速度较快，一旦密钥发生变动则需要进行多轮运算计算 sub keys，可以有效防止 key 被爆破
- 加密过程实现简单，相对DES加密来说速度更快
