| 1 | .TH CRYPT 3
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| 2 | .SH NAME
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| 3 | crypt \- one-way password encryption function
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| 4 | .SH SYNOPSIS
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| 5 | .ft B
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| 6 | .nf
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| 7 | #define _MINIX_SOURCE 1
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| 8 | #include <unistd.h>
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| 9 |
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| 10 | char *crypt(const char *\fIkey\fP, const char *\fIsalt\fP)
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| 11 | .fi
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| 12 | .ft P
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| 13 | .SH DESCRIPTION
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| 14 | The first use of
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| 15 | .B crypt()
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| 16 | is to encrypt a password. Its second use is to authenticate a shadow
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| 17 | password. In both cases
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| 18 | .B crypt()
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| 19 | calls
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| 20 | .BR pwdauth (8)
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| 21 | to do the real work.
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| 22 | .PP
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| 23 | .B Crypt()
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| 24 | encrypts a password if called with a user typed key, and a salt
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| 25 | whose first two characters are in the set [./0-9A-Za-z]. The result is a
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| 26 | character string in the [./0-9A-Za-z] alphabet of which the first two
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| 27 | characters are equal to the salt, and the rest is the result of encrypting
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| 28 | the key and the salt.
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| 29 | .PP
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| 30 | If
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| 31 | .B crypt()
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| 32 | is called with a salt that has the form
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| 33 | .BI "##" user
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| 34 | then the key is encrypted and compared to the encrypted password of
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| 35 | .I user
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| 36 | in the shadow password file. If they are equal then
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| 37 | .B crypt()
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| 38 | returns the
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| 39 | .BI "##" user
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| 40 | argument, if not then some other string is returned. This trick assures
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| 41 | that the normal way to authenticate a password still works:
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| 42 | .PP
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| 43 | .RS
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| 44 | .nf
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| 45 | if (strcmp(pw->pw_passwd, crypt(key, pw->pw_passwd))) ...
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| 46 | .fi
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| 47 | .RE
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| 48 | .PP
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| 49 | If
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| 50 | .I key
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| 51 | is a null string, and the shadow password is a null string or the salt is a
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| 52 | null string then the result equals
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| 53 | .IR salt .
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| 54 | (This is because the caller can't tell if a password field is empty in the
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| 55 | shadow password file.)
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| 56 | .PP
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| 57 | The key and salt are limited to 1024 bytes total including the null bytes.
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| 58 | .SH FILES
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| 59 | .TP 25
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| 60 | /usr/lib/pwdauth
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| 61 | The password authentication program
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| 62 | .SH "SEE ALSO"
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| 63 | .BR getpass (3),
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| 64 | .BR getpwent (3),
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| 65 | .BR passwd (5),
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| 66 | .BR pwdauth (8).
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| 67 | .SH NOTES
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| 68 | The result of an encryption is returned in a static array that is
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| 69 | overwritten by each call. The return value should not be modified.
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| 70 | .SH AUTHOR
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| 71 | Kees J. Bot (kjb@cs.vu.nl)
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