1 /* PAK is an encrypted key exchange protocol designed by Philip MacKenzie et al. */
2 /* It is patented and use outside Plan 9 requires you get a license. */
3 /* (All other EKE protocols are patented as well, by Lucent or others.) */
4 #include <u.h>
5 #include <libc.h>
6 #include <mp.h>
7 #include <libsec.h>
8 #include "SConn.h"
9 #include "secstore.h"
10 
11 extern int verbose;
12 
13 char VERSION[] = "secstore";
14 static char *feedback[] = {"alpha","bravo","charlie","delta","echo","foxtrot","golf","hotel"};
15 
16 typedef struct PAKparams{
17 	mpint *q, *p, *r, *g;
18 } PAKparams;
19 
20 static PAKparams *pak;
21 
22 /* from seed EB7B6E35F7CD37B511D96C67D6688CC4DD440E1E */
23 static void
24 initPAKparams(void)
25 {
26 	if(pak)
27 		return;
28 	pak = (PAKparams*)emalloc(sizeof(*pak));
29 	pak->q = strtomp("E0F0EF284E10796C5A2A511E94748BA03C795C13", nil, 16, nil);
30 	pak->p = strtomp("C41CFBE4D4846F67A3DF7DE9921A49D3B42DC33728427AB159CEC8CBB"
31 		"DB12B5F0C244F1A734AEB9840804EA3C25036AD1B61AFF3ABBC247CD4B384224567A86"
32 		"3A6F020E7EE9795554BCD08ABAD7321AF27E1E92E3DB1C6E7E94FAAE590AE9C48F96D9"
33 		"3D178E809401ABE8A534A1EC44359733475A36A70C7B425125062B1142D",
34 		nil, 16, nil);
35 	pak->r = strtomp("DF310F4E54A5FEC5D86D3E14863921E834113E060F90052AD332B3241"
36 		"CEF2497EFA0303D6344F7C819691A0F9C4A773815AF8EAECFB7EC1D98F039F17A32A7E"
37 		"887D97251A927D093F44A55577F4D70444AEBD06B9B45695EC23962B175F266895C67D"
38 		"21C4656848614D888A4", nil, 16, nil);
39 	pak->g = strtomp("2F1C308DC46B9A44B52DF7DACCE1208CCEF72F69C743ADD4D23271734"
40 		"44ED6E65E074694246E07F9FD4AE26E0FDDD9F54F813C40CB9BCD4338EA6F242AB94CD"
41 		"410E676C290368A16B1A3594877437E516C53A6EEE5493A038A017E955E218E7819734"
42 		"E3E2A6E0BAE08B14258F8C03CC1B30E0DDADFCF7CEDF0727684D3D255F1",
43 		nil, 16, nil);
44 }
45 
46 /* H = (sha(ver,C,sha(passphrase)))^r mod p, */
47 /* a hash function expensive to attack by brute force. */
48 static void
49 longhash(char *ver, char *C, uchar *passwd, mpint *H)
50 {
51 	uchar *Cp;
52 	int i, n, nver, nC;
53 	uchar buf[140], key[1];
54 
55 	nver = strlen(ver);
56 	nC = strlen(C);
57 	n = nver + nC + SHA1dlen;
58 	Cp = (uchar*)emalloc(n);
59 	memmove(Cp, ver, nver);
60 	memmove(Cp+nver, C, nC);
61 	memmove(Cp+nver+nC, passwd, SHA1dlen);
62 	for(i = 0; i < 7; i++){
63 		key[0] = 'A'+i;
64 		hmac_sha1(Cp, n, key, sizeof key, buf+i*SHA1dlen, nil);
65 	}
66 	memset(Cp, 0, n);
67 	free(Cp);
68 	betomp(buf, sizeof buf, H);
69 	mpmod(H, pak->p, H);
70 	mpexp(H, pak->r, pak->p, H);
71 }
72 
73 /* Hi = H^-1 mod p */
74 char *
75 PAK_Hi(char *C, char *passphrase, mpint *H, mpint *Hi)
76 {
77 	uchar passhash[SHA1dlen];
78 
79 	sha1((uchar *)passphrase, strlen(passphrase), passhash, nil);
80 	initPAKparams();
81 	longhash(VERSION, C, passhash, H);
82 	mpinvert(H, pak->p, Hi);
83 	return mptoa(Hi, 64, nil, 0);
84 }
85 
86 /* another, faster, hash function for each party to */
87 /* confirm that the other has the right secrets. */
88 static void
89 shorthash(char *mess, char *C, char *S, char *m, char *mu, char *sigma, char *Hi, uchar *digest)
90 {
91 	SHA1state *state;
92 
93 	state = sha1((uchar*)mess, strlen(mess), 0, 0);
94 	state = sha1((uchar*)C, strlen(C), 0, state);
95 	state = sha1((uchar*)S, strlen(S), 0, state);
96 	state = sha1((uchar*)m, strlen(m), 0, state);
97 	state = sha1((uchar*)mu, strlen(mu), 0, state);
98 	state = sha1((uchar*)sigma, strlen(sigma), 0, state);
99 	state = sha1((uchar*)Hi, strlen(Hi), 0, state);
100 	state = sha1((uchar*)mess, strlen(mess), 0, state);
101 	state = sha1((uchar*)C, strlen(C), 0, state);
102 	state = sha1((uchar*)S, strlen(S), 0, state);
103 	state = sha1((uchar*)m, strlen(m), 0, state);
104 	state = sha1((uchar*)mu, strlen(mu), 0, state);
105 	state = sha1((uchar*)sigma, strlen(sigma), 0, state);
106 	sha1((uchar*)Hi, strlen(Hi), digest, state);
107 }
108 
109 /* On input, conn provides an open channel to the server; */
110 /*	C is the name this client calls itself; */
111 /*	pass is the user's passphrase */
112 /* On output, session secret has been set in conn */
113 /*	(unless return code is negative, which means failure). */
114 /*    If pS is not nil, it is set to the (alloc'd) name the server calls itself. */
115 int
116 PAKclient(SConn *conn, char *C, char *pass, char **pS)
117 {
118 	char *mess, *mess2, *eol, *S, *hexmu, *ks, *hexm, *hexsigma = nil, *hexHi;
119 	char kc[2*SHA1dlen+1];
120 	uchar digest[SHA1dlen];
121 	int rc = -1, n;
122 	mpint *x, *m = mpnew(0), *mu = mpnew(0), *sigma = mpnew(0);
123 	mpint *H = mpnew(0), *Hi = mpnew(0);
124 
125 	hexHi = PAK_Hi(C, pass, H, Hi);
126 	if(verbose)
127 		fprint(2,"%s\n", feedback[H->p[0]&0x7]);  /* provide a clue to catch typos */
128 
129 	/* random 1<=x<=q-1; send C, m=g**x H */
130 	x = mprand(240, genrandom, nil);
131 	mpmod(x, pak->q, x);
132 	if(mpcmp(x, mpzero) == 0)
133 		mpassign(mpone, x);
134 	mpexp(pak->g, x, pak->p, m);
135 	mpmul(m, H, m);
136 	mpmod(m, pak->p, m);
137 	hexm = mptoa(m, 64, nil, 0);
138 	mess = (char*)emalloc(2*Maxmsg+2);
139 	mess2 = mess+Maxmsg+1;
140 	snprint(mess, Maxmsg, "%s\tPAK\nC=%s\nm=%s\n", VERSION, C, hexm);
141 	conn->write(conn, (uchar*)mess, strlen(mess));
142 
143 	/* recv g**y, S, check hash1(g**xy) */
144 	if(readstr(conn, mess) < 0){
145 		fprint(2, "error: %s\n", mess);
146 		writerr(conn, "couldn't read g**y");
147 		goto done;
148 	}
149 	eol = strchr(mess, '\n');
150 	if(strncmp("mu=", mess, 3) != 0 || !eol || strncmp("\nk=", eol, 3) != 0){
151 		writerr(conn, "verifier syntax error");
152 		goto done;
153 	}
154 	hexmu = mess+3;
155 	*eol = 0;
156 	ks = eol+3;
157 	eol = strchr(ks, '\n');
158 	if(!eol || strncmp("\nS=", eol, 3) != 0){
159 		writerr(conn, "verifier syntax error for secstore 1.0");
160 		goto done;
161 	}
162 	*eol = 0;
163 	S = eol+3;
164 	eol = strchr(S, '\n');
165 	if(!eol){
166 		writerr(conn, "verifier syntax error for secstore 1.0");
167 		goto done;
168 	}
169 	*eol = 0;
170 	if(pS)
171 		*pS = estrdup(S);
172 	strtomp(hexmu, nil, 64, mu);
173 	mpexp(mu, x, pak->p, sigma);
174 	hexsigma = mptoa(sigma, 64, nil, 0);
175 	shorthash("server", C, S, hexm, hexmu, hexsigma, hexHi, digest);
176 	enc64(kc, sizeof kc, digest, SHA1dlen);
177 	if(strcmp(ks, kc) != 0){
178 		writerr(conn, "verifier didn't match");
179 		goto done;
180 	}
181 
182 	/* send hash2(g**xy) */
183 	shorthash("client", C, S, hexm, hexmu, hexsigma, hexHi, digest);
184 	enc64(kc, sizeof kc, digest, SHA1dlen);
185 	snprint(mess2, Maxmsg, "k'=%s\n", kc);
186 	conn->write(conn, (uchar*)mess2, strlen(mess2));
187 
188 	/* set session key */
189 	shorthash("session", C, S, hexm, hexmu, hexsigma, hexHi, digest);
190 	memset(hexsigma, 0, strlen(hexsigma));
191 	n = conn->secret(conn, digest, 0);
192 	memset(digest, 0, SHA1dlen);
193 	if(n < 0){
194 		writerr(conn, "can't set secret");
195 		goto done;
196 	}
197 
198 	rc = 0;
199 done:
200 	mpfree(x);
201 	mpfree(sigma);
202 	mpfree(mu);
203 	mpfree(m);
204 	mpfree(Hi);
205 	mpfree(H);
206 	free(hexsigma);
207 	free(hexHi);
208 	free(hexm);
209 	free(mess);
210 	return rc;
211 }
212 
213 /* On input, */
214 /*	mess contains first message; */
215 /*	name is name this server should call itself. */
216 /* On output, session secret has been set in conn; */
217 /*	if pw!=nil, then *pw points to PW struct for authenticated user. */
218 /*	returns -1 if error */
219 int
220 PAKserver(SConn *conn, char *S, char *mess, PW **pwp)
221 {
222 	int rc = -1, n;
223 	char mess2[Maxmsg+1], *eol;
224 	char *C, ks[41], *kc, *hexm, *hexmu = nil, *hexsigma = nil, *hexHi = nil;
225 	uchar digest[SHA1dlen];
226 	mpint *H = mpnew(0), *Hi = mpnew(0);
227 	mpint *y = nil, *m = mpnew(0), *mu = mpnew(0), *sigma = mpnew(0);
228 	PW *pw = nil;
229 
230 	/* secstore version and algorithm */
231 	snprint(mess2,Maxmsg,"%s\tPAK\n", VERSION);
232 	n = strlen(mess2);
233 	if(strncmp(mess,mess2,n) != 0){
234 		writerr(conn, "protocol should start with ver alg");
235 		return -1;
236 	}
237 	mess += n;
238 	initPAKparams();
239 
240 	/* parse first message into C, m */
241 	eol = strchr(mess, '\n');
242 	if(strncmp("C=", mess, 2) != 0 || !eol){
243 		fprint(2,"mess[1]=%s\n", mess);
244 		writerr(conn, "PAK version mismatch");
245 		goto done;
246 	}
247 	C = mess+2;
248 	*eol = 0;
249 	hexm = eol+3;
250 	eol = strchr(hexm, '\n');
251 	if(strncmp("m=", hexm-2, 2) != 0 || !eol){
252 		writerr(conn, "PAK version mismatch");
253 		goto done;
254 	}
255 	*eol = 0;
256 	strtomp(hexm, nil, 64, m);
257 	mpmod(m, pak->p, m);
258 
259 	/* lookup client */
260 	if((pw = getPW(C,0)) == nil) {
261 		snprint(mess2, sizeof mess2, "%r");
262 		writerr(conn, mess2);
263 		goto done;
264 	}
265 	if(mpcmp(m, mpzero) == 0) {
266 		writerr(conn, "account exists");
267 		freePW(pw);
268 		pw = nil;
269 		goto done;
270 	}
271 	hexHi = mptoa(pw->Hi, 64, nil, 0);
272 
273 	/* random y, mu=g**y, sigma=g**xy */
274 	y = mprand(240, genrandom, nil);
275 	mpmod(y, pak->q, y);
276 	if(mpcmp(y, mpzero) == 0){
277 		mpassign(mpone, y);
278 	}
279 	mpexp(pak->g, y, pak->p, mu);
280 	mpmul(m, pw->Hi, m);
281 	mpmod(m, pak->p, m);
282 	mpexp(m, y, pak->p, sigma);
283 
284 	/* send g**y, hash1(g**xy) */
285 	hexmu = mptoa(mu, 64, nil, 0);
286 	hexsigma = mptoa(sigma, 64, nil, 0);
287 	shorthash("server", C, S, hexm, hexmu, hexsigma, hexHi, digest);
288 	enc64(ks, sizeof ks, digest, SHA1dlen);
289 	snprint(mess2, sizeof mess2, "mu=%s\nk=%s\nS=%s\n", hexmu, ks, S);
290 	conn->write(conn, (uchar*)mess2, strlen(mess2));
291 
292 	/* recv hash2(g**xy) */
293 	if(readstr(conn, mess2) < 0){
294 		writerr(conn, "couldn't read verifier");
295 		goto done;
296 	}
297 	eol = strchr(mess2, '\n');
298 	if(strncmp("k'=", mess2, 3) != 0 || !eol){
299 		writerr(conn, "verifier syntax error");
300 		goto done;
301 	}
302 	kc = mess2+3;
303 	*eol = 0;
304 	shorthash("client", C, S, hexm, hexmu, hexsigma, hexHi, digest);
305 	enc64(ks, sizeof ks, digest, SHA1dlen);
306 	if(strcmp(ks, kc) != 0) {
307 		rc = -2;
308 		goto done;
309 	}
310 
311 	/* set session key */
312 	shorthash("session", C, S, hexm, hexmu, hexsigma, hexHi, digest);
313 	n = conn->secret(conn, digest, 1);
314 	if(n < 0){
315 		writerr(conn, "can't set secret");
316 		goto done;
317 	}
318 
319 	rc = 0;
320 done:
321 	if(rc<0 && pw){
322 		pw->failed++;
323 		putPW(pw);
324 	}
325 	if(rc==0 && pw && pw->failed>0){
326 		pw->failed = 0;
327 		putPW(pw);
328 	}
329 	if(pwp)
330 		*pwp = pw;
331 	else
332 		freePW(pw);
333 	free(hexsigma);
334 	free(hexHi);
335 	free(hexmu);
336 	mpfree(y);
337 	mpfree(sigma);
338 	mpfree(mu);
339 	mpfree(m);
340 	mpfree(Hi);
341 	mpfree(H);
342 	return rc;
343 }
344