{ "cells": [ { "cell_type": "markdown", "source": [ "\"Cryptographie" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "# TP3. Cryptographie appliquée\n", "\n", "Dans ce TP nous travaillerons en Python 3, directement à l'intérieur de ce notebook jupyter.\n", "\n", "Nous avons choisi d'utiliser la bibliothèque [PyCryptodome](http://www.pycryptodome.org/). Pour rejouer cette fiche en dehors du TP, il convient d'installer une version récente de [PyCryptodome](http://www.pycryptodome.org/) sur votre système.\n", "\n", "L'objectif du TP est d'expérimenter des éléments vus en cours et en TD dans deux cas pratique. Ces deux exemples sont inspirés du Challenge de crypto 2019/2020." ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "## 1. Chiffrement de VPN avec IPSec\n", "\n", "[IPsec](http://fr.wikipedia.org/wiki/Internet_Protocol_Security) offre un mécanisme normalisé et donc interopérable de chiffrement des données en mode host-to-host ou lan-to-lan (avec tunnel). L'ensemble des RFCs décrivant IPsec est touffu, on se contentera de lire dans un premier temps la [page Wikipedia IPsec](http://en.wikipedia.org/wiki/IPsec) et dans un second temps seulement [An Illustrated Guide to IPsec](http://www.unixwiz.net/techtips/iguide-ipsec.html).\n", "\n", "Le protocole [IKE](https://fr.wikipedia.org/wiki/Internet_Key_Exchange) permet de négocier les paramètres de connexion. C'est la bonne manière d'utiliser IPSec. Dans ce TP, afin de nous focaliser sur le mécanisme de chiffrement des paquets, nous avons opté pour une configuration statique du VPN en manipulant directement la configuration noyau à l'aide de la commande `ip`.\n", "\n", "Dans cet exercice, il s'agit de comprendre les grands principes d'IPSec afin de décoder des échanges réseau chiffrés à partir de la connaissance des paramètres cryptographiques utilisés. En effet, l'avantage d'un protocole normalisé est d'être débugable, ici à l'aide de [Wireshark](https://www.wireshark.org).\n" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "Téléchargez le [fichier pcap](https://pdicost.univ-orleans.fr/cryptodm/micmac.php?user=110&data=7&apikey=ee6d2b7a1338ded6267165f91b5a860643f5df5442e2885584b17841d8e7bb6f) à ouvrir dans Wireshark." ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "L'objectif est de pouvoir accéder au contenu en clair des paquets comme sur la copie d'écran ci-dessous.\n", "\n", "PS. Le fichier pcap correspond à une écoute sur toutes les interfaces d'un routeur intermédiaire, chaque trame apparait donc dupliquée. Pour que ce soit plus lisible, vous pouvez par exemple utiliser le même filtre que sur la copie d'écran.\n", "\n", "![une fois déchiffré](https://pdicost.univ-orleans.fr/cryptodm/micmac.php?user=110&data=8&apikey=037f1e32a51ef99c259f0271c0d6366fa136ce7e1e8b615317969f70a6ca572c)" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "Voici le script qui a été utilisé pour configurer un des routeurs qui mettent en place le tunnel IPSec.\n", "\n", "\n", "```bash\n", "#!/bin/sh\n", "####### STATE\n", "ip xfrm state flush\n", "ip xfrm state add src 100.10.10.10 dst 100.20.20.20 \\\n", "\tproto esp spi 0x539 mode tunnel \\\n", "\tenc \"cbc(aes)\" \"micmac is sha256\" \\\n", "\tauth-trunc \"hmac(md5)\" \"(K+M) which is v\" 96\n", "ip xfrm state add src 100.20.20.20 dst 100.10.10.10 \\\n", "\tproto esp spi 0x539 mode tunnel \\\n", "\tenc \"cbc(aes)\" \"ulnerable to len\" \\\n", "\tauth-trunc \"hmac(md5)\" \"gth extension at\" 96\n", "###### POLICY\n", "ip xfrm policy flush\n", "ip xfrm policy add src 192.168.2.0/24 dst 192.168.1.0/24 \\\n", "\tdir fwd tmpl src 100.20.20.20 dst 100.10.10.10 \\\n", "\t\tproto esp mode tunnel\n", "ip xfrm policy add src 192.168.2.0/24 dst 192.168.1.0/24 \\\n", "\tdir in tmpl src 100.20.20.20 dst 100.10.10.10 \\\n", "\t\tproto esp mode tunnel\n", "ip xfrm policy add src 192.168.1.0/24 dst 192.168.2.0/24 \\\n", "\tdir out tmpl src 100.10.10.10 dst 100.20.20.20 \\\n", "\t\tproto esp mode tunnel\n", "\n", "```" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "En vous aidant de la [documentation de Wireshark sur l'écoute IPSec](https://gitlab.com/wireshark/wireshark/-/wikis/ESP_Preferences), déchiffrez l'échange TCP entre Alice et Bob !" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "## 2. Qu'est-ce que c'est que ce micmac ?\n", "\n", "Observez les URLs utilisées pour obtenir le fichier pcap et les copies d'écran ci-dessus, par exemple `https://pdicost.univ-orleans.fr/cryptodm/micmac.php?user=110&data=8&apikey=037f1e32a51ef99c259f0271c0d6366fa136ce7e1e8b615317969f70a6ca572c`\n", "\n", "Elles sont servies par un script PHP dont voici le code source :\n" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "```\n", "prepare('SELECT secret FROM users WHERE user = :user');\n", " $st->bindParam(':user',$user);\n", " $res=$st->execute();\n", " $secret=\"FAIL\";\n", " while($x = $res->fetchArray(SQLITE3_NUM)) $secret=hex2bin($x[0]);\n", " if (strlen($secret) !== 32) fail();\n", " // Check if the API key is correct for that URL\n", " $s=urldecode($_SERVER['QUERY_STRING']);\n", " $pos=strpos($s, \"&apikey=\");\n", " if ($pos !== false) {\n", " $h=substr($s,$pos+8);\n", " $s=substr($s,0,$pos);\n", " }\n", " $hh=hash('sha256',$secret . $s);\n", " if (strcmp($h,$hh) !== 0) fail();\n", " // Ok we are good, we can provide the data if it exists in the DB\n", " $st=$db->prepare('SELECT mimetype FROM files WHERE rowid = :data');\n", " $st->bindParam(':data',$data);\n", " $res=$st->execute();\n", " $mimetype=FALSE;\n", " while($x = $res->fetchArray(SQLITE3_NUM)) { $mimetype=$x[0]; }\n", " if ($mimetype === FALSE) fail();\n", " $f=$db->openBlob('files', 'content', $data);\n", " header('Content-Type: ' . $mimetype);\n", " while(!feof($f)) echo fread($f,8192);\n", " fclose($f);\n", "?>\n", "```" ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "Les URLs sont du type `https://pdicost.univ-orleans.fr/cryptodm/micmac.php?user=👩‍🦰&data=#️⃣&apikey=🍰` où le champ `apikey` contient en hexadécimal la valeur `SHA256(K+M)` avec `K` un secret de 32 octets et `M` la chaîne `user=👩‍🦰&data=#️⃣` (du caractère qui suit le `?` jusqu'au pied de `&apikey`).\n", "\n", "Comme nous l'avons vu en cours, une attaque par extension de longueur est possible sur `SHA256`. Ici, elle va nous permettre d'accéder à toutes les paires de valeur `(user,data)` que l'on souhaite en construisant des URLs de la forme : `https://pdicost.univ-orleans.fr/cryptodm/micmac.php?user=👩‍🦰&data=#️⃣PADDING&data=NOUVELLEVALEUR&apikey=NOUVEAUMICMAC`.\n", "\n", "À vous de jouer : trouvez une URL valide pour accéder à la ressource `data=3`.\n", "\n", "Pour vous aider dans votre tâche, voici le code source d'une mise en œuvre en Python de SHA256." ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "code", "source": [ "SHA_BLOCKSIZE = 64\n", "SHA_DIGESTSIZE = 32\n", "\n", "\n", "def new_shaobject():\n", " return {\n", " 'digest': [0]*8,\n", " 'count_lo': 0,\n", " 'count_hi': 0,\n", " 'data': [0]* SHA_BLOCKSIZE,\n", " 'local': 0,\n", " 'digestsize': 0\n", " }\n", "\n", "ROR = lambda x, y: (((x & 0xffffffff) >> (y & 31)) | (x << (32 - (y & 31)))) & 0xffffffff\n", "Ch = lambda x, y, z: (z ^ (x & (y ^ z)))\n", "Maj = lambda x, y, z: (((x | y) & z) | (x & y))\n", "S = lambda x, n: ROR(x, n)\n", "R = lambda x, n: (x & 0xffffffff) >> n\n", "Sigma0 = lambda x: (S(x, 2) ^ S(x, 13) ^ S(x, 22))\n", "Sigma1 = lambda x: (S(x, 6) ^ S(x, 11) ^ S(x, 25))\n", "Gamma0 = lambda x: (S(x, 7) ^ S(x, 18) ^ R(x, 3))\n", "Gamma1 = lambda x: (S(x, 17) ^ S(x, 19) ^ R(x, 10))\n", "\n", "def sha_transform(sha_info):\n", " W = []\n", " \n", " d = sha_info['data']\n", " for i in range(0,16):\n", " W.append( (d[4*i]<<24) + (d[4*i+1]<<16) + (d[4*i+2]<<8) + d[4*i+3])\n", " \n", " for i in range(16,64):\n", " W.append( (Gamma1(W[i - 2]) + W[i - 7] + Gamma0(W[i - 15]) + W[i - 16]) & 0xffffffff )\n", " \n", " ss = sha_info['digest'][:]\n", " \n", " def RND(a,b,c,d,e,f,g,h,i,ki):\n", " t0 = h + Sigma1(e) + Ch(e, f, g) + ki + W[i];\n", " t1 = Sigma0(a) + Maj(a, b, c);\n", " d += t0;\n", " h = t0 + t1;\n", " return d & 0xffffffff, h & 0xffffffff\n", " \n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],0,0x428a2f98);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],1,0x71374491);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],2,0xb5c0fbcf);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],3,0xe9b5dba5);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],4,0x3956c25b);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],5,0x59f111f1);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],6,0x923f82a4);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],7,0xab1c5ed5);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],8,0xd807aa98);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],9,0x12835b01);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],10,0x243185be);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],11,0x550c7dc3);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],12,0x72be5d74);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],13,0x80deb1fe);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],14,0x9bdc06a7);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],15,0xc19bf174);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],16,0xe49b69c1);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],17,0xefbe4786);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],18,0x0fc19dc6);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],19,0x240ca1cc);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],20,0x2de92c6f);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],21,0x4a7484aa);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],22,0x5cb0a9dc);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],23,0x76f988da);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],24,0x983e5152);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],25,0xa831c66d);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],26,0xb00327c8);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],27,0xbf597fc7);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],28,0xc6e00bf3);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],29,0xd5a79147);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],30,0x06ca6351);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],31,0x14292967);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],32,0x27b70a85);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],33,0x2e1b2138);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],34,0x4d2c6dfc);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],35,0x53380d13);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],36,0x650a7354);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],37,0x766a0abb);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],38,0x81c2c92e);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],39,0x92722c85);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],40,0xa2bfe8a1);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],41,0xa81a664b);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],42,0xc24b8b70);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],43,0xc76c51a3);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],44,0xd192e819);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],45,0xd6990624);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],46,0xf40e3585);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],47,0x106aa070);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],48,0x19a4c116);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],49,0x1e376c08);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],50,0x2748774c);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],51,0x34b0bcb5);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],52,0x391c0cb3);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],53,0x4ed8aa4a);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],54,0x5b9cca4f);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],55,0x682e6ff3);\n", " ss[3], ss[7] = RND(ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],56,0x748f82ee);\n", " ss[2], ss[6] = RND(ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],57,0x78a5636f);\n", " ss[1], ss[5] = RND(ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],ss[5],58,0x84c87814);\n", " ss[0], ss[4] = RND(ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],ss[4],59,0x8cc70208);\n", " ss[7], ss[3] = RND(ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],ss[3],60,0x90befffa);\n", " ss[6], ss[2] = RND(ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],ss[2],61,0xa4506ceb);\n", " ss[5], ss[1] = RND(ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],ss[1],62,0xbef9a3f7);\n", " ss[4], ss[0] = RND(ss[1],ss[2],ss[3],ss[4],ss[5],ss[6],ss[7],ss[0],63,0xc67178f2);\n", " \n", " dig = []\n", " for i, x in enumerate(sha_info['digest']):\n", " dig.append( (x + ss[i]) & 0xffffffff )\n", " sha_info['digest'] = dig\n", "\n", "def sha_init():\n", " sha_info = new_shaobject()\n", " sha_info['digest'] = [0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19]\n", " sha_info['count_lo'] = 0\n", " sha_info['count_hi'] = 0\n", " sha_info['local'] = 0\n", " sha_info['digestsize'] = 32\n", " return sha_info\n", "\n", "def sha_update(sha_info, buffer):\n", " if isinstance(buffer, str):\n", " raise TypeError(\"Unicode strings must be encoded before hashing\")\n", " count = len(buffer)\n", " buffer_idx = 0\n", " clo = (sha_info['count_lo'] + (count << 3)) & 0xffffffff\n", " if clo < sha_info['count_lo']:\n", " sha_info['count_hi'] += 1\n", " sha_info['count_lo'] = clo\n", " \n", " sha_info['count_hi'] += (count >> 29)\n", " \n", " if sha_info['local']:\n", " i = SHA_BLOCKSIZE - sha_info['local']\n", " if i > count:\n", " i = count\n", " \n", " # copy buffer\n", " sha_info['data'][sha_info['local']:sha_info['local']+i] = buffer[buffer_idx:buffer_idx+i]\n", " \n", " count -= i\n", " buffer_idx += i\n", " \n", " sha_info['local'] += i\n", " if sha_info['local'] == SHA_BLOCKSIZE:\n", " sha_transform(sha_info)\n", " sha_info['local'] = 0\n", " else:\n", " return\n", " \n", " while count >= SHA_BLOCKSIZE:\n", " # copy buffer\n", " sha_info['data'] = list(buffer[buffer_idx:buffer_idx + SHA_BLOCKSIZE])\n", " count -= SHA_BLOCKSIZE\n", " buffer_idx += SHA_BLOCKSIZE\n", " sha_transform(sha_info)\n", " \n", " \n", " # copy buffer\n", " pos = sha_info['local']\n", " sha_info['data'][pos:pos+count] = buffer[buffer_idx:buffer_idx + count]\n", " sha_info['local'] = count\n", "\n", "def sha_final(sha_info):\n", " lo_bit_count = sha_info['count_lo']\n", " hi_bit_count = sha_info['count_hi']\n", " count = (lo_bit_count >> 3) & 0x3f\n", " sha_info['data'][count] = 0x80;\n", " count += 1\n", " if count > SHA_BLOCKSIZE - 8:\n", " # zero the bytes in data after the count\n", " sha_info['data'] = sha_info['data'][:count] + ([0] * (SHA_BLOCKSIZE - count))\n", " sha_transform(sha_info)\n", " # zero bytes in data\n", " sha_info['data'] = [0] * SHA_BLOCKSIZE\n", " else:\n", " sha_info['data'] = sha_info['data'][:count] + ([0] * (SHA_BLOCKSIZE - count))\n", " \n", " sha_info['data'][56] = (hi_bit_count >> 24) & 0xff\n", " sha_info['data'][57] = (hi_bit_count >> 16) & 0xff\n", " sha_info['data'][58] = (hi_bit_count >> 8) & 0xff\n", " sha_info['data'][59] = (hi_bit_count >> 0) & 0xff\n", " sha_info['data'][60] = (lo_bit_count >> 24) & 0xff\n", " sha_info['data'][61] = (lo_bit_count >> 16) & 0xff\n", " sha_info['data'][62] = (lo_bit_count >> 8) & 0xff\n", " sha_info['data'][63] = (lo_bit_count >> 0) & 0xff\n", " \n", " sha_transform(sha_info)\n", " \n", " dig = []\n", " for i in sha_info['digest']:\n", " dig.extend([ ((i>>24) & 0xff), ((i>>16) & 0xff), ((i>>8) & 0xff), (i & 0xff) ])\n", " return bytes(dig)\n", "\n", "class sha256(object):\n", " digest_size = digestsize = SHA_DIGESTSIZE\n", " block_size = SHA_BLOCKSIZE\n", "\n", " def __init__(self, s=None):\n", " self.name = 'sha256'\n", " self._sha = sha_init()\n", " if s:\n", " sha_update(self._sha, s)\n", " \n", " def update(self, s):\n", " sha_update(self._sha, s)\n", " \n", " def digest(self):\n", " return sha_final(self._sha.copy())[:self._sha['digestsize']]\n", " \n", " def hexdigest(self):\n", " return ''.join(['%.2x' % i for i in self.digest()])\n", "\n", " def copy(self):\n", " new = sha256.__new__(sha256)\n", " new._sha = self._sha.copy()\n", " return new\n" ], "outputs": [], "execution_count": 1, "metadata": { "execution": { "iopub.execute_input": "2020-11-26T15:47:16.914Z", "iopub.status.busy": "2020-11-26T15:47:16.873Z", "iopub.status.idle": "2020-11-26T15:47:16.953Z", "shell.execute_reply": "2020-11-26T15:47:16.987Z" }, "jupyter": { "outputs_hidden": false, "source_hidden": false }, "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "code", "source": [ "# exemple d'utilisation\n", "dgst=sha256(b\"The cake is a lie.\")\n", "print(dgst.hexdigest())\n", "print(\"État de l'algorithme :\",dgst._sha)" ], "outputs": [ { "output_type": "stream", "name": "stdout", "text": [ "0f802c63154b269693741bfd54ec01ab6b2a07abe748c46f60be1eb1a36a1729\n", "État de l'algorithme : {'digest': [1779033703, 3144134277, 1013904242, 2773480762, 1359893119, 2600822924, 528734635, 1541459225], 'count_lo': 144, 'count_hi': 0, 'data': [84, 104, 101, 32, 99, 97, 107, 101, 32, 105, 115, 32, 97, 32, 108, 105, 101, 46, 128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], 'local': 18, 'digestsize': 32}\n" ] } ], "execution_count": 4, "metadata": { "execution": { "iopub.execute_input": "2020-11-26T15:47:27.827Z", "iopub.status.busy": "2020-11-26T15:47:27.814Z", "iopub.status.idle": "2020-11-26T15:47:27.875Z", "shell.execute_reply": "2020-11-26T15:47:27.913Z" }, "jupyter": { "outputs_hidden": false, "source_hidden": false }, "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "markdown", "source": [ "Suggestion de plan de bataille :\n", " - écrire une fonction de padding `pad(msglen)` qui retourne le padding utilisé pour un message de longueur `msglen` ;\n", " - écrire une fonction `sha_cont(msglen,hexdgst)` qui, à partir d'une longueur de message `msglen` et d'une empreinte SHA256 `hexdgst` du message donnée en hexadécimal, retourne une instance de la classe `sha256` prête à recevoir de nouvelles `update` : toute l'astuce consiste à construire un dictionnaire `_sha` correspondant à l'état de l'algorithme après padding ;\n", " - en déduire une fonction `extend(msglen,hexdgst,more)` qui à partir de la longueur `msglen`, de l'empreinte `hexdgst` et d'une chaîne supplémentaire `more`, retourne la chaîne `pad(msglen)+more` et l'empreinte du message étendu par cette chaîne." ], "metadata": { "nteract": { "transient": { "deleting": false } } } }, { "cell_type": "code", "source": [], "outputs": [], "execution_count": null, "metadata": { "collapsed": true, "jupyter": { "source_hidden": false, "outputs_hidden": false }, "nteract": { "transient": { "deleting": false } } } } ], "metadata": { "kernel_info": { "name": "python3" }, "kernelspec": { "display_name": "Python 3", "language": "python", "name": "python3" }, "language_info": { "name": "python", "version": "3.6.12", "mimetype": "text/x-python", "codemirror_mode": { "name": "ipython", "version": 3 }, "pygments_lexer": "ipython3", "nbconvert_exporter": "python", "file_extension": ".py" }, "nteract": { "version": "0.26.0" } }, "nbformat": 4, "nbformat_minor": 1 }