+/********************************************************
+* prvs: Get last three digits of days since Jan 1, 1970 *
+********************************************************/
+
+/* This is needed to implement the "prvs" BATV reverse
+ path signing scheme
+
+Argument: integer "days" offset to add or substract to
+ or from the current number of days.
+
+Returns: pointer to string containing the last three
+ digits of the number of days since Jan 1, 1970,
+ modified by the offset argument, NULL if there
+ was an error in the conversion.
+
+*/
+
+static uschar *
+prvs_daystamp(int day_offset)
+{
+uschar *days = store_get(32); /* Need at least 24 for cases */
+(void)string_format(days, 32, TIME_T_FMT, /* where TIME_T_FMT is %lld */
+ (time(NULL) + day_offset*86400)/86400);
+return (Ustrlen(days) >= 3) ? &days[Ustrlen(days)-3] : US"100";
+}
+
+
+
+/********************************************************
+* prvs: perform HMAC-SHA1 computation of prvs bits *
+********************************************************/
+
+/* This is needed to implement the "prvs" BATV reverse
+ path signing scheme
+
+Arguments:
+ address RFC2821 Address to use
+ key The key to use (must be less than 64 characters
+ in size)
+ key_num Single-digit key number to use. Defaults to
+ '0' when NULL.
+
+Returns: pointer to string containing the first three
+ bytes of the final hash in hex format, NULL if
+ there was an error in the process.
+*/
+
+static uschar *
+prvs_hmac_sha1(uschar *address, uschar *key, uschar *key_num, uschar *daystamp)
+{
+uschar *hash_source, *p;
+int size = 0,offset = 0,i;
+sha1 sha1_base;
+void *use_base = &sha1_base;
+uschar innerhash[20];
+uschar finalhash[20];
+uschar innerkey[64];
+uschar outerkey[64];
+uschar *finalhash_hex = store_get(40);
+
+if (key_num == NULL)
+ key_num = US"0";
+
+if (Ustrlen(key) > 64)
+ return NULL;
+
+hash_source = string_cat(NULL,&size,&offset,key_num,1);
+string_cat(hash_source,&size,&offset,daystamp,3);
+string_cat(hash_source,&size,&offset,address,Ustrlen(address));
+hash_source[offset] = '\0';
+
+DEBUG(D_expand) debug_printf("prvs: hash source is '%s'\n", hash_source);
+
+memset(innerkey, 0x36, 64);
+memset(outerkey, 0x5c, 64);
+
+for (i = 0; i < Ustrlen(key); i++)
+ {
+ innerkey[i] ^= key[i];
+ outerkey[i] ^= key[i];
+ }
+
+chash_start(HMAC_SHA1, use_base);
+chash_mid(HMAC_SHA1, use_base, innerkey);
+chash_end(HMAC_SHA1, use_base, hash_source, offset, innerhash);
+
+chash_start(HMAC_SHA1, use_base);
+chash_mid(HMAC_SHA1, use_base, outerkey);
+chash_end(HMAC_SHA1, use_base, innerhash, 20, finalhash);
+
+p = finalhash_hex;
+for (i = 0; i < 3; i++)
+ {
+ *p++ = hex_digits[(finalhash[i] & 0xf0) >> 4];
+ *p++ = hex_digits[finalhash[i] & 0x0f];
+ }
+*p = '\0';
+
+return finalhash_hex;
+}
+
+
+
+