jbn@wdl1.UUCP (John B. Nagle) (04/19/84)
/*
Obvious password detection subroutine.
Call:
char word[];
char *obvious(word);
Returns 0 if password is acceptable.
Returns a pointer to a static message if the password is unacceptable.
The algorithm used requires that the length of the password be
within configurable length limits, and that the password not
have triplet statistics similar to those associated with words
in the English language. This is an inversion of a technique
used to find spelling errors without a full dictionary. No
word in the UNIX spelling dictionary will pass this algorithm.
Users should be advised to pick a password composed of random
letters and numbers. Eight randomly chosen letters will
pass the algorithm over 95% of the time. A word prefaced
by a digit will not pass the algorithm, although a word
with a digit in the middle usually will. Two words run
together will often pass.
In the interest of greater network security, this algorithm
is offered to the ARPANET community as a proposed standard technique
for eliminating obvious passwords.
John Nagle
Ford Aerospace and Communications Corporation
Western Development Laboratories
3939 Fabian Way
Palo Alto, CA 94303
1/16/84
*/
/*
Table of triple usage in text
24511 words were used to make this table.
The words came from the files:
/usr/dict/words
obvpats.lp
The table is 30 percent populated.
*/
long obvtab[27][27] =
{
{ 0X00100001, 0X00040000, 0X00040000, 0X00009000, 0X00808020, 0X00140000,
0X00000000, 0X00080000, 0X00000002, 0X00000000, 0X00000000, 0X00000000,
0X00001020, 0X00000000, 0X00000010, 0X00000020, 0X00000000, 0X00000000,
0X00000030, 0X00300100, 0X00000100, 0X00000000, 0X00000020, 0X00000000,
0X00000000, 0X00000000, 0X00000000 },
{ 0X00090000, 0X000c708a, 0X022cd73e, 0X023ffbbe, 0X02fffffe, 0X002cd0da,
0X023cdae2, 0X02adf3b6, 0X0024f222, 0X00dd7efa, 0X00008022, 0X02b5937a,
0X06fdfbfe, 0X02bdf37e, 0X07ffdfff, 0X003c3248, 0X023dfb76, 0X00200000,
0X07fffffe, 0X02bbfbbe, 0X06bcfb6f, 0X055f7dfc, 0X02609232, 0X021cfbf6,
0X02999222, 0X00bdf3ff, 0X06308232 },
{ 0X00080000, 0X07fdfbfc, 0X022c9226, 0X00008012, 0X00248222, 0X07dffbfe,
0X00200000, 0X00000000, 0X00208020, 0X047ffdfe, 0X00000020, 0X00000000,
0X02208222, 0X00800220, 0X0000a022, 0X03fdfffe, 0X00048000, 0X00000000,
0X02208222, 0X00308228, 0X00049062, 0X071efefc, 0X00000220, 0X00000020,
0X00000000, 0X049d11a2, 0X00000000 },
{ 0X00080080, 0X02fffffe, 0X000c0020, 0X0024932a, 0X0000802a, 0X06bdf3fe,
0X00000002, 0X00248220, 0X02bdf3fe, 0X007df0fe, 0X00000000, 0X02bdfffe,
0X02208222, 0X00200222, 0X00008222, 0X07fffffe, 0X00000102, 0X00200000,
0X02308222, 0X00188200, 0X02aca262, 0X003df27e, 0X00000004, 0X00000000,
0X00000000, 0X001dd08e, 0X00000022 },
{ 0X00088022, 0X06fd7bfc, 0X02249222, 0X00209102, 0X02249332, 0X07fff7fe,
0X00249282, 0X02a43a22, 0X00008222, 0X05fdf3fe, 0X00208022, 0X00000220,
0X02208222, 0X00208222, 0X00008223, 0X07fdf3fe, 0X00049322, 0X00200000,
0X02208222, 0X0091bb2a, 0X00008302, 0X043dfafe, 0X00008222, 0X02048222,
0X00000000, 0X00987aef, 0X00200000 },
{ 0X004c1030, 0X04ff79dc, 0X023c9226, 0X023c9b3a, 0X02bdf3fe, 0X04ddfbfe,
0X023c92fa, 0X0224f3e6, 0X0224a222, 0X045d7afa, 0X00208022, 0X0218ca36,
0X02fdfbfe, 0X02a9f22e, 0X06ffffff, 0X05fd73d8, 0X02bdb32e, 0X00200000,
0X07fffffe, 0X02fbfbbe, 0X06bdfb6e, 0X005d78bc, 0X066c8222, 0X029df37e,
0X0333832a, 0X008df97f, 0X06648222 },
{ 0X00080000, 0X07bc7bfe, 0X00000222, 0X0000000a, 0X00008002, 0X02fc7abe,
0X022cb366, 0X00000102, 0X00000022, 0X055c70fe, 0X00008000, 0X00000002,
0X02208222, 0X0000000a, 0X00000200, 0X03edf2be, 0X00000008, 0X00000000,
0X02208222, 0X00118922, 0X028ca32e, 0X041c74b8, 0X00000000, 0X00000002,
0X00000000, 0X00000000, 0X00000000 },
{ 0X00080000, 0X06fdf3fc, 0X00008222, 0X00000000, 0X00008022, 0X02fdf3fe,
0X00240220, 0X020d93a2, 0X02bddffe, 0X047df0fe, 0X00000002, 0X00008200,
0X02208222, 0X02300222, 0X00318226, 0X02fdf3fe, 0X00009220, 0X00000000,
0X02208222, 0X00919b06, 0X00048302, 0X061cf2ee, 0X00000000, 0X02048022,
0X00000000, 0X00056002, 0X00000002 },
{ 0X00080000, 0X06fdfbfe, 0X02249222, 0X00048102, 0X00048202, 0X07fff2ff,
0X00208202, 0X00008022, 0X00008122, 0X047dfcfe, 0X00000800, 0X00008220,
0X02248222, 0X0008a222, 0X0028c222, 0X06fdfeff, 0X00209202, 0X00200000,
0X02249232, 0X00108302, 0X02bdf3fa, 0X071d71fe, 0X00000200, 0X00008322,
0X00000000, 0X011d32be, 0X00000000 },
{ 0X00483010, 0X05dd7bbc, 0X022cf226, 0X023cdb2a, 0X02bdf6b6, 0X04fd79fc,
0X0234d262, 0X063df3a2, 0X00000222, 0X00000202, 0X00208002, 0X02208a22,
0X02fdbbfe, 0X022df36e, 0X07ffffff, 0X05fd70be, 0X02bdb766, 0X00200000,
0X02fdfafe, 0X02ffffff, 0X06bdfb6f, 0X000c7008, 0X02248222, 0X00008202,
0X023082e2, 0X00000002, 0X04608022 },
{ 0X00080000, 0X07ed7bbc, 0X00000000, 0X00000000, 0X00000000, 0X009cd57a,
0X00000000, 0X00000000, 0X00000000, 0X005070c4, 0X00000400, 0X00001000,
0X00000000, 0X00000000, 0X00000000, 0X02fc5bae, 0X00000000, 0X00000000,
0X00000000, 0X00000000, 0X00000000, 0X015d7e96, 0X00000000, 0X00000000,
0X00000000, 0X00000000, 0X00000000 },
{ 0X00080000, 0X07fdfff4, 0X00248222, 0X00040302, 0X00048022, 0X02fdf3f6,
0X00208222, 0X00048000, 0X0014a022, 0X00ddf8fe, 0X00000002, 0X0000ca22,
0X0220a222, 0X00000022, 0X00208222, 0X01fdfb7a, 0X00009202, 0X00000000,
0X02208222, 0X02b1abae, 0X00048302, 0X029d7110, 0X00000000, 0X00008322,
0X00000000, 0X00ac9522, 0X00000000 },
{ 0X00088000, 0X07fffbfe, 0X02249222, 0X0234b322, 0X02bdf36e, 0X07fdfffe,
0X00bc93e6, 0X00048222, 0X00008222, 0X05fffdfe, 0X00008000, 0X0288d322,
0X02bdb7fe, 0X0228e332, 0X00208020, 0X07fffffe, 0X021ca362, 0X00000000,
0X02208022, 0X0299ab26, 0X06eca326, 0X055dfefe, 0X00008222, 0X02008322,
0X00000000, 0X00bdfbfe, 0X00000022 },
{ 0X00080000, 0X07fdffbc, 0X002dd236, 0X0021fbfe, 0X00008020, 0X07ddfbfe,
0X00209220, 0X00000000, 0X00208020, 0X053efcfa, 0X00000000, 0X00000000,
0X00008222, 0X0220a222, 0X02208222, 0X07fdfbfe, 0X023c9be6, 0X00200000,
0X00088002, 0X0239a37c, 0X00048120, 0X041dfaf8, 0X00000020, 0X00008222,
0X00000000, 0X001cd0a8, 0X00000000 },
{ 0X00180000, 0X06fdfbfe, 0X002c922a, 0X02349b22, 0X02bffffe, 0X07fff3ff,
0X00249222, 0X02bdbb76, 0X02208222, 0X057ffbfe, 0X00208022, 0X021d33ea,
0X02008222, 0X00008222, 0X0228c222, 0X07fdf2fe, 0X00209220, 0X00200000,
0X0220822a, 0X02fdfbfe, 0X06adf3ee, 0X043dfafe, 0X02208222, 0X00048322,
0X00100200, 0X01ffb11e, 0X02808222 },
{ 0X0008113c, 0X017f79da, 0X02fcd77e, 0X02349b2a, 0X02adfbfe, 0X037ef35c,
0X0234b262, 0X02bcf7f6, 0X0204f222, 0X011c58fe, 0X00008222, 0X02a99b2e,
0X06fdfbfe, 0X02aff36e, 0X07ffffff, 0X045df9dc, 0X02bffbae, 0X00200000,
0X06fffbfe, 0X02fbbbae, 0X02bdf3ee, 0X055f73ff, 0X02008a22, 0X06bdfb7e,
0X02d043ea, 0X001dd37e, 0X06008222 },
{ 0X00080000, 0X07fffabc, 0X002c9022, 0X00008100, 0X00040002, 0X07fdfefe,
0X00241220, 0X00040002, 0X023cd232, 0X057ff8fa, 0X00000002, 0X00000220,
0X02208222, 0X00208022, 0X00008020, 0X03fdfafa, 0X022db322, 0X00040000,
0X02208222, 0X02b0bb2a, 0X0224832a, 0X041d7afe, 0X00000008, 0X00048202,
0X00000000, 0X00949b86, 0X00000000 },
{ 0X00080000, 0X00100000, 0X00000000, 0X00000000, 0X00000000, 0X00000010,
0X00000000, 0X00000000, 0X00000000, 0X00000000, 0X00000000, 0X00000000,
0X00000000, 0X00000000, 0X00000000, 0X00000000, 0X00000000, 0X00020000,
0X00080000, 0X00000000, 0X00000000, 0X02008222, 0X00000000, 0X00000020,
0X00000000, 0X00000000, 0X00000000 },
{ 0X00080010, 0X07fffffc, 0X022c9222, 0X023c9b2a, 0X02bdd366, 0X07ffffff,
0X00249222, 0X022cb322, 0X02208222, 0X07fbfdfe, 0X00208020, 0X029df336,
0X02b98236, 0X0239936e, 0X02b9ab66, 0X07fffffe, 0X023cb322, 0X00200000,
0X02248322, 0X02f3fb7e, 0X06bcf3ee, 0X01ddf2fe, 0X02208222, 0X00008222,
0X00000020, 0X0099f0be, 0X00008222 },
{ 0X00081000, 0X03fdfffe, 0X02248222, 0X0224b323, 0X00248242, 0X07fffbfe,
0X02208222, 0X002c8220, 0X02f5fa6e, 0X057ff8fe, 0X00200000, 0X0224a222,
0X02208222, 0X02208222, 0X02208223, 0X06f5f7fe, 0X022c9326, 0X00200000,
0X00288222, 0X02bdf36e, 0X02edf7ff, 0X041df2fe, 0X00010220, 0X00248222,
0X00000000, 0X001d78bc, 0X00000000 },
{ 0X001c1010, 0X03fdfbfc, 0X00248222, 0X02249102, 0X00048000, 0X03fdfbfe,
0X00249222, 0X00248022, 0X02bffbfe, 0X047ff8fe, 0X00000000, 0X02000222,
0X02208222, 0X00208222, 0X00308223, 0X07fdfafe, 0X00049222, 0X00000000,
0X02a08222, 0X02f1ab7e, 0X027c9be2, 0X031df2fe, 0X00000202, 0X01208322,
0X00000000, 0X01ad328e, 0X000db2a2 },
{ 0X004c1010, 0X02dd7bdc, 0X027db736, 0X023c9b2a, 0X06ac92b6, 0X063df5f6,
0X0030b042, 0X002cf3a2, 0X00004002, 0X057dd0be, 0X00208202, 0X00048a30,
0X06fdfafe, 0X007bf36e, 0X02bdfbfe, 0X023d5210, 0X02bdbbfe, 0X00200000,
0X06fffbfe, 0X023bdbbe, 0X06bcf3be, 0X00202000, 0X00840220, 0X00000002,
0X00309220, 0X00601022, 0X04208022 },
{ 0X00080000, 0X003d7fbc, 0X00004000, 0X00000000, 0X00000002, 0X039dfbfe,
0X00000000, 0X00000000, 0X00000000, 0X057cdafe, 0X00000000, 0X00000100,
0X00008002, 0X00000000, 0X00000000, 0X02bcfa88, 0X00000000, 0X00000000,
0X00008020, 0X00000800, 0X00000000, 0X000c1000, 0X02400220, 0X01000000,
0X00000000, 0X00800200, 0X00008000 },
{ 0X00080000, 0X077d7bde, 0X00248222, 0X00208102, 0X02248220, 0X025d53bf,
0X00209202, 0X00000200, 0X02208222, 0X055d70f8, 0X00000000, 0X02804200,
0X02180222, 0X00000222, 0X02bd03fc, 0X00fdf864, 0X00209222, 0X00000000,
0X02008222, 0X02bdbb2c, 0X00208322, 0X00057100, 0X00000000, 0X00808002,
0X02000000, 0X0000f022, 0X02000000 },
{ 0X00080000, 0X005870d8, 0X00000000, 0X00649322, 0X00000000, 0X021c7298,
0X00008000, 0X00201000, 0X00208202, 0X0058f0fe, 0X00000000, 0X00000000,
0X00000020, 0X00000000, 0X00000002, 0X001d6090, 0X00249222, 0X00200000,
0X00000000, 0X00000020, 0X02248326, 0X00051016, 0X00000200, 0X00008020,
0X01008000, 0X04041080, 0X00000000 },
{ 0X004c1010, 0X0097f998, 0X00248232, 0X00009322, 0X0004c226, 0X00ddf0f6,
0X00201222, 0X0224f230, 0X02048020, 0X00094030, 0X00000002, 0X00004420,
0X00699a22, 0X0221e22e, 0X0310c3ba, 0X04fd78d8, 0X023dd322, 0X00200000,
0X0234c272, 0X0039b32e, 0X02108322, 0X00095b88, 0X00000022, 0X0004832a,
0X00000200, 0X02000000, 0X00000002 },
{ 0X00080000, 0X00557b8e, 0X00000000, 0X00000000, 0X00000002, 0X00bc5a3e,
0X00000000, 0X00000020, 0X00000000, 0X003df0ae, 0X00000000, 0X00000000,
0X02008020, 0X00000002, 0X00000000, 0X0065e2b2, 0X00000002, 0X00000000,
0X00008002, 0X00000008, 0X00000020, 0X00040820, 0X00008020, 0X00008020,
0X00000008, 0X00002084, 0X06809222 } };
/*
Configuration parameters
*/
#define MINLENGTH 5 /* minimum password length */
#define MAXLENGTH 8 /* maximum password length */
#define MINNOFIND 2 /* minimum unusual triples */
short unusual; /* count of unusual triples */
/*
obvious -- test word for obviousness as password
Words are rejected for being too short, too long,
or looking too much like English words.
*/
char *obvious(word) /* returns msg or zero if OK */
char word[]; /* word to try */
{
register int i = 0; /* for length */
while (word[i]) i++; /* compute length */
if (i < MINLENGTH) return("too short");
if (i > MAXLENGTH) return("too long");
unusual = 0; /* no unusual triples yet */
obvword(word); /* try the word */
if (unusual<MINNOFIND) return("too obvious"); /* too obvious */
return(0); /* success */
}
/*
dotriple -- called by obvword
If this triple is not used by any word used to build the table,
we tally that fact.
*/
dotriple(m1,m2,m3)
short m1,m2,m3; /* all in 0..26 */
{
if (!(obvtab[m1][m2] & (1L << m3))) unusual++; /* check for triple */
}
/*
obvword -- do one word
dotriple is called on each 3-character triple in the word,
using a mapped value of the character into the range 0..26,
where letters map into 1..26 regardless of case and everything
else maps to zero.
*/
obvword(word)
char word[]; /* word to do, max 20 chars */
{ register int i; /* for loops */
register int patcnt = 0; /* count in word */
register char ch; /* working char */
short pat[21]; /* pattern of mapped values */
for (i=0; word[i] && (i < sizeof(pat)); i++) /* scan until null */
{ patcnt = i; /* max value */
ch = word[i]; /* get character */
if ((ch >= 'a') && (ch <= 'z')) pat[i] = ch + 1 - 'a';
else if ((ch >= 'A') && (ch <= 'Z')) pat[i] = ch + 1 - 'A';
else pat[i] = 0; /* map into 0..26 */
}
for (i=0; i < patcnt - 1; i++) /* for all triples */
{ dotriple(pat[i],pat[i+1],pat[i+2]); /* do the triple */
}
}