add doc for ASN.1 GeneralizedTime

crypt.tex

@@ -4692,16 +4692,18 @@ LTC_SET_ASN1(sequence, x++, LTC_ASN1_NULL,           NULL,   0);
 \hline LTC\_ASN1\_NULL               & NULL \\
 \hline LTC\_ASN1\_OBJECT\_IDENTIFIER & OBJECT IDENTIFIER  \\
 \hline LTC\_ASN1\_IA5\_STRING        & IA5 STRING (one octet per char) \\
-\hline LTC\_ASN1\_UTF8\_STRING       & UTF8 STRING (one wchar\_t per char) \\
 \hline LTC\_ASN1\_PRINTABLE\_STRING  & PRINTABLE STRING (one octet per char) \\
+\hline LTC\_ASN1\_UTF8\_STRING       & UTF8 STRING (one wchar\_t per char) \\
 \hline LTC\_ASN1\_UTCTIME            & UTCTIME (see ltc\_utctime structure) \\
+\hline LTC\_ASN1\_CHOICE             & CHOICE \\
 \hline LTC\_ASN1\_SEQUENCE           & SEQUENCE (and SEQUENCE OF) \\
 \hline LTC\_ASN1\_SET                & SET \\
 \hline LTC\_ASN1\_SETOF              & SET OF \\
-\hline LTC\_ASN1\_CHOICE             & CHOICE \\
 \hline LTC\_ASN1\_RAW\_BIT\_STRING   & BIT STRING (one octet per char) \\
 \hline LTC\_ASN1\_TELETEX\_STRING    & TELETEX STRING (one octet per char) \\
 \hline LTC\_ASN1\_CONSTRUCTED        & A constructed type that is not SEQUENCE or SET \\
+\hline LTC\_ASN1\_CONTEXT\_SPECIFIC  & A context-specific type \\
+\hline LTC\_ASN1\_GENERALIZEDTIME    & GeneralizedTime (see ltc\_generalizedtime structure) \\
 \hline
 \end{tabular}
 \caption{List of ASN.1 Supported Types}
@@ -5141,6 +5143,57 @@ input.  The decoder will read all valid ASN.1 formats and perform range checking
 
 It is suggested that decoded data be further scrutinized (e.g. days of month in particular).
 
+\subsection{ASN.1 GeneralizedTime}
+
+The GeneralizedTime type is to store a date and time in ASN.1 format.  It uses the following structure to organize the time.
+
+\index{ltc\_utctime structure}
+\begin{verbatim}
+typedef struct {
+   unsigned YYYY, /* year              0--9999 */
+            MM, /* month               1--12 */
+            DD, /* day                 1--31 */
+            hh, /* hour                0--23 */
+            mm, /* minute              0--59 */
+            ss, /* second              0--59 */
+            fs, /* fractional seconds  1--UINT_MAX */
+            off_dir, /* timezone offset direction 0 == +, 1 == - */
+            off_hh, /* timezone offset hours */
+            off_mm; /* timezone offset minutes */
+} ltc_generalizedtime;
+\end{verbatim}
+
+The time can be offset plus or minus a set amount of hours (off\_hh) and minutes (off\_mm).  When \textit{off\_dir} is zero, the time will be added otherwise it
+will be subtracted.  For instance, the array $\lbrace 2005, 6, 20, 22, 4, 0, 122, 0, 5, 0 \rbrace$ represents the current time of
+\textit{2005, June 20th, 22:04:00.122} with a time offset of +05h00.
+
+\index{der\_encode\_utctime()}\index{der\_decode\_utctime()}\index{der\_length\_utctime()}
+\begin{verbatim}
+int der_encode_generalizedtime(ltc_generalizedtime *gtime,
+                               unsigned char       *out,
+                               unsigned long       *outlen);
+
+int der_decode_generalizedtime(const unsigned char *in,
+                               unsigned long       *inlen,
+                               ltc_generalizedtime *out);
+
+int der_length_generalizedtime(ltc_generalizedtime *gtime,
+                               unsigned long       *outlen);
+\end{verbatim}
+
+The encoder will store time in one of the following ASN.1 formats, either \textit{YYYYMMDDhhmmssZ} or
+\textit{YYYYMMDDhhmmss$\pm$hhmm} or\textit{YYYYMMDDhhmmss.fsZ} or \textit{YYYYMMDDhhmmss.fs$\pm$hhmm},
+and perform minimal error checking on the input.
+The decoder will read all valid ASN.1 formats and perform range checking on the values (not complete but
+rational) useful for catching packet errors.
+
+The fractional seconds are always added in case they are not $0$.
+The implementation of fractional seconds is currently unreliable and you can't detect decoded
+resp. encode leading $0$'s (e.g. \textit{20170424232717.005Z} would be decoded as
+\textit{22. April 2017, 23:27:17.5}).
+
+It is suggested that decoded data be further scrutinized (e.g. days of month in particular).
+
 \subsection{ASN.1 CHOICE}
 
 The CHOICE ASN.1 type represents a union of ASN.1 types all of which are stored in a \textit{ltc\_asn1\_list}.  There is no encoder for the CHOICE type, only a