93 řádků
2,2 KiB
C
93 řádků
2,2 KiB
C
/*
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* otpcli - command-line interface for HOTP and TOTP
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* Written in 2020-2021 by Lucas
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*
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* To the extent possible under law, the author(s) have dedicated all
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* copyright and related and neighboring rights to this software to the
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* public domain worldwide. This software is distributed without any
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* warranty.
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*
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* You should have received a copy of the CC0 Public Domain Dedication
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* along with this software. If not, see
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* <http://creativecommons.org/publicdomain/zero/1.0/>.
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*/
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#include <limits.h>
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#include <openssl/hmac.h>
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#include "otp.h"
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int32_t
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otp(const struct otpcfg *otpcfg)
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{
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const EVP_MD *evp_md;
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unsigned char md_value[EVP_MAX_MD_SIZE];
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uint8_t buf[8];
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uint64_t counter;
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uint32_t res;
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int32_t modulo;
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unsigned int digits, md_len, offset;
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switch (otpcfg->type) {
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case OTP_HOTP:
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counter = otpcfg->u.hotp.counter;
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break;
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case OTP_TOTP:
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if (otpcfg->u.totp.period == 0)
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return -1;
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counter = otpcfg->u.totp.time / otpcfg->u.totp.period;
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break;
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default:
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return -1;
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}
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switch (otpcfg->algorithm) {
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case OTP_HMAC_SHA1:
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evp_md = EVP_sha1();
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break;
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case OTP_HMAC_SHA256:
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evp_md = EVP_sha256();
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break;
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case OTP_HMAC_SHA512:
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evp_md = EVP_sha512();
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break;
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default:
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return -1;
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}
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digits = otpcfg->digits;
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if (digits < 6 || digits > 10)
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return -1;
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/*
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* 10 digits would be 10_000_000_000, which overflows 32 bits.
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* Nevertheless, given the number construction, 10 digits OTP are
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* possible. We won't apply reminder operator in that case.
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*/
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if (digits < 10)
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for (modulo = 1000000; digits > 6; digits--, modulo *= 10)
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continue;
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/* convert counter to big endian */
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buf[0] = counter >> 56;
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buf[1] = (counter >> 48) & 0xff;
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buf[2] = (counter >> 40) & 0xff;
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buf[3] = (counter >> 32) & 0xff;
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buf[4] = (counter >> 24) & 0xff;
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buf[5] = (counter >> 16) & 0xff;
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buf[6] = (counter >> 8) & 0xff;
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buf[7] = counter & 0xff;
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if (HMAC(evp_md, otpcfg->secret, otpcfg->secretlen, buf, sizeof(buf),
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md_value, &md_len) == NULL)
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return -1;
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offset = md_value[md_len - 1] & 0xf;
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res = (md_value[offset] << 24) |
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(md_value[offset + 1] << 16) |
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(md_value[offset + 2] << 8) |
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md_value[offset + 3];
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res &= 0x7fffffff;
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return digits == 10 ? (int32_t)res : (int32_t)res % modulo;
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}
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