Preliminary ASN1_TIME documentation.
Reviewed-by: Rich Salz <rsalz@openssl.org>
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Dr. Stephen Henson
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doc/crypto/ASN1_TIME_set.pod
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doc/crypto/ASN1_TIME_set.pod
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=pod
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=head1 NAME
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ASN1_TIME_set, ASN1_TIME_adj, ASN1_TIME_check, ASN1_TIME_set_string,
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ASN1_TIME_print, ASN1_TIME_diff - ASN.1 Time functions.
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=head1 SYNOPSIS
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ASN1_TIME *ASN1_TIME_set(ASN1_TIME *s, time_t t);
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ASN1_TIME *ASN1_TIME_adj(ASN1_TIME *s, time_t t,
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int offset_day, long offset_sec);
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int ASN1_TIME_set_string(ASN1_TIME *s, const char *str);
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int ASN1_TIME_check(const ASN1_TIME *t);
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int ASN1_TIME_print(BIO *b, const ASN1_TIME *s);
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int ASN1_TIME_diff(int *pday, int *psec,
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const ASN1_TIME *from, const ASN1_TIME *to);
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=head1 DESCRIPTION
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The function ASN1_TIME_set() sets the ASN1_TIME structure B<s> to the
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time represented by the time_t value B<t>. If B<s> is NULL a new ASN1_TIME
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structure is allocated and returned.
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ASN1_TIME_adj() sets the ASN1_TIME structure B<s> to the time represented
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by the time B<offset_day> and B<offset_sec> after the time_t value B<t>.
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The values of B<offset_day> or B<offset_sec> can be negative to set a
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time before B<t>. The B<offset_sec> value can also exceed the number of
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seconds in a day. If B<s> is NULL a new ASN1_TIME structure is allocated
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and returned.
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ASN1_TIME_set_string() sets ASN1_TIME structure B<s> to the time
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represented by string B<str> which must be in appropriate ASN.1 time
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format (for example YYMMDDHHMMSSZ or YYYYMMDDHHMMSSZ).
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ASN1_TIME_check() checks the syntax of ASN1_TIME structure B<s>.
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ASN1_TIME_print() prints out the time B<s> to BIO B<b> in human readable
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format. It will be of the format MMM DD HH:MM:SS YYYY [GMT], for example
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"Feb 3 00:55:52 2015 GMT" it does not include a newline. If the time
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structure has invalid format it prints out "Bad time value" and returns
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an error.
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ASN1_TIME_diff() sets B<*pday> and B<*psec> to the time difference between
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B<from> and B<to>. If B<to> represents a time later than B<from> then
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one or both (depending on the time difference) of B<*pday> and B<*psec>
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will be positive. If B<to> represents a time earlier than B<from> then
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one or both of B<*pday> and B<*psec> will be negative. If B<to> and B<from>
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represent the same time then B<*pday> and B<*psec> will both be zero.
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If both B<*pday> and B<*psec> are non-zero they will always have the same
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sign. The value of B<*psec> will always be less than the number of seconds
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in a day. If B<from> or B<to> is NULL the current time is used.
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=head1 NOTES
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The ASN1_TIME structure corresponds to the ASN.1 structure B<Time>
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defined in RFC5280 et al. The time setting functions obey the rules outlined
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in RFC5280: if the date can be represented by UTCTime it is used, else
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GeneralizedTime is used.
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The ASN1_TIME structure is represented as an ASN1_STRING internally and can
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be freed up using ASN1_STRING_free().
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The ASN1_TIME structure can represent years from 0000 to 9999 but no attempt
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is made to correct ancient calendar changes (for example from Julian to
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Gregorian calendars).
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Some applications add offset times directly to a time_t value and pass the
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results to ASN1_TIME_set() (or equivalent). This can cause problems as the
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time_t value can overflow on some systems resulting in unexpected results.
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New applications should use ASN1_TIME_adj() instead and pass the offset value
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in the B<offset_sec> and B<offset_day> parameters instead of directly
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manipulating a time_t value.
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=head1 BUGS
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ASN1_TIME_print() currently does not print out the time zone: it either prints
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out "GMT" or nothing. But all certificates complying with RFC5280 et al use GMT
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anyway.
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=head1 EXAMPLES
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Set a time structure to one hour after the current time and print it out:
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#include <time.h>
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#include <openssl/asn1.h>
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ASN1_TIME *tm;
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time_t t;
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BIO *b;
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t = time(NULL);
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tm = ASN1_TIME_adj(NULL, t, 0, 60 * 60);
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b = BIO_new_fp(stdout, BIO_NOCLOSE);
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ASN1_TIME_print(b, tm);
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ASN1_STRING_free(tm);
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BIO_free(b);
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Determine if one time is later or sooner than the current time:
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int day, sec;
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if (!ASN1_TIME_diff(&day, &sec, NULL, to))
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/* Invalid time format */
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if (day > 0 || sec > 0)
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printf("Later\n");
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else if (day < 0 || sec < 0)
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printf("Sooner\n");
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else
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printf("Same\n");
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=head1 RETURN VALUES
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ASN1_TIME_set() and ASN1_TIME_adj() return a pointer to an ASN1_TIME structure
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or NULL if an error occurred.
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ASN1_TIME_set_string() returns 1 if the time value is successfully set and
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0 otherwise.
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ASN1_TIME_check() returns 1 if the structure is syntactically correct and 0
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otherwise.
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ASN1_TIME_print() returns 1 if the time is successfully printed out and 0 if
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an error occurred (I/O error or invalid time format).
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ASN1_TIME_diff() returns 1 for sucess and 0 for failure. It can fail if the
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pass ASN1_TIME structure has invalid syntax for example.
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=cut
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