Of counter values above starting_counter will also be checked if If resync_resync is greater than 0, some number The starting_counter should be the counter of the last successfulĪuthentication plus 1. std :: pair verify_hotp ( uint32_t otp, uint64_t starting_counter, size_t resync_range = 0 ) ¶Ĭheck if a provided OTP matches the one that should be generated for Return the OTP associated with a specific counter value. uint32_t generate_hotp ( uint64_t counter ) ¶ On SHA-1 do not have any known effect on HOTP’s security. Implementations support SHA-256 as an extension. In RFC 4226, HOTP is only defined with SHA-1, but many HOTP ![]() Initialize an HOTP instance with a secret key (specific to each client),Ī hash algorithm (must be SHA-1, SHA-256, or SHA-512), and the number ofĭigits with each OTP (must be 6, 7, or 8). Implement counter-based OTP HOTP ( const SymmetricKey & key, const std :: string & hash_algo = "SHA-1", size_t digits = 6 ) ¶ Given to any other symmetric key or plaintext password. Thus both client and server must keep track of the next counterĪnyone with access to the client-specific secret key can authenticate as thatĬlient, so it should be treated with the same security consideration as would be Must assure the counter only increments and is never repeated orĭecremented. If the counter ever repeats the OTP will also repeat, thus both parties (most applications use 6 digits), created using the HMAC of a 64-bit counter HOTP generates OTPs that are a short numeric sequence, between 6 and 8 digits Otherwise an attackerĬould quickly try all 1000000 6-digit OTPs in a brief amount of time. ![]() OTP authentication attempts to some small number per second. Since the range of possible OTPs is quite small, applications must rate limit Password (or a public key signature) and an OTP generated by a small device suchīotan implements the HOTP and TOTP schemes from RFC 42. Commonly this is used to implement two-factorĪuthentication (2FA), where the user authenticates using both a conventional One time password schemes are a user authentication method that relies on aįixed secret key which is used to derive a sequence of short passwords, each of
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