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Rewrite the luhn algorithm to be faster and easier to read. See #69.

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This commit is contained in:
brectanus 2007-12-01 00:42:28 +00:00
parent 13e209909f
commit 9e9bb318b3
1 changed files with 27 additions and 35 deletions
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56
apache2/re_operators.c
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@ -918,55 +918,47 @@ static int msre_op_validateSchema_execute(modsec_rec *msr, msre_rule *rule, msre
/* verifyCC */ /* verifyCC */
static int validate_cc (modsec_rec *msr, const char *ccnumber, int len) { /**
* Luhn Mod-10 Method (ISO 2894/ANSI 4.13)
*/
static int luhn_verify(const char *ccnumber, int len) {
char ccdigits[16]; char ccdigits[16];
char *cdst = ccdigits; char *cdst = ccdigits;
const char *csrc = ccnumber; const char *csrc = ccnumber;
int digits = 0; int digits = 0;
int srclen = 0; int srclen = 0;
int multiply;
int digit;
int add;
int sum = 0; int sum = 0;
int weight;
int i;
/* Remove non digits characters */ /* Weighted lookup table which is just a precalculated (i = index):
* i*2 + (( (i*2) > 9 ) ? -9 : 0)
*/
static int wtable[10] = {0, 2, 4, 6, 8, 1, 3, 5, 7, 9}; /* weight lookup table */
/* Remove non digits characters and calculate the true length */
while ((srclen++ <= len) && (digits < 16)) { while ((srclen++ <= len) && (digits < 16)) {
if (isdigit(*csrc)) { if (isdigit(*csrc)) {
*(cdst++) = *csrc - 48; *(cdst++) = *csrc;
++digits; ++digits;
} }
csrc++; csrc++;
msr_log(msr, 9, "cdst[%d]: %.*s", digits, digits, ccdigits);
} }
/* Credit card checksum algorithm */ /* Determine if the first digit is weighted: odd=no, even=yes */
weight = !(digits & 1);
for (digit = digits - 1, multiply = 0; digit >= 0; digit--) { /* Add up digits (weighted digits via lookup table) */
if (multiply) { for (i = 0; i < digits; i++) {
add = ccdigits[digit] * 2; sum += (weight ? wtable[ccdigits[i] - '0'] : (ccdigits[i] - '0'));
} weight = !weight; /* alternate weights */
else {
add = ccdigits[digit];
}
if (add > 9) {
sum += add - 9;
}
else {
sum += add;
}
multiply = 1 - multiply;
} }
/* See if the final digit is a zero, if so the card is valid. */ /* Do a mod 10 on the sum */
if ((sum % 10) != 0) { sum %= 10;
return 0;
} else { /* If the result is a zero the card is valid. */
return 1; return sum ? 0 : 1;
}
} }
static int msre_op_verifyCC_init(msre_rule *rule, char **error_msg) { static int msre_op_verifyCC_init(msre_rule *rule, char **error_msg) {
@ -1062,7 +1054,7 @@ static int msre_op_verifyCC_execute(modsec_rec *msr, msre_rule *rule, msre_var *
msr_log(msr, 9, "Adding regex subexpression to TXVARS (%i): %s", k, msr_log(msr, 9, "Adding regex subexpression to TXVARS (%i): %s", k,
log_escape_nq(msr->mp, s->value)); log_escape_nq(msr->mp, s->value));
if ((k > 0) && validate_cc (msr, s->value, s->value_len)) { if ((k > 0) && luhn_verify (s->value, s->value_len)) {
is_cc = 1; is_cc = 1;
} }
} }