1 files changed, 52 insertions, 0 deletions
diff --git a/src/lib/misc/hotp/hotp.h b/src/lib/misc/hotp/hotp.h
new file mode 100644
index 000000000..cc222e5c0
--- /dev/null
+++ b/src/lib/misc/hotp/hotp.h
@@ -0,0 +1,52 @@
+/*
+* HOTP
+* (C) 2017 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#ifndef BOTAN_HOTP_H__
+#define BOTAN_HOTP_H__
+
+#include <botan/mac.h>
+
+namespace Botan {
+
+/**
+* HOTP one time passwords (RFC 4226)
+*/
+class BOTAN_DLL HOTP
+   {
+   public:
+      /**
+      * @param key the secret key shared between client and server
+      * @param hash_algo the hash algorithm to use, should be SHA-1 or SHA-256
+      * @param digits the number of digits in the OTP (must be 6, 7, or 8)
+      */
+      HOTP(const SymmetricKey& key, const std::string& hash_algo = "SHA-1", size_t digits = 6);
+
+      /**
+      * Generate the HOTP for a particular counter value
+      * @warning if the counter value is repeated the OTP ceases to be one-time
+      */
+      uint32_t generate_hotp(uint64_t counter);
+
+      /**
+      * Check an OTP value using a starting counter and a resync range
+      * @param otp the client provided OTP
+      * @param starting_counter the server's guess as to the current counter state
+      * @param resync_range if 0 then only HOTP(starting_counter) is accepted
+      * If larger than 0, up to resync_range values after HOTP are also checked.
+      * @return (valid,next_counter). If the OTP does not validate, always
+      * returns (false,starting_counter). Otherwise returns (true,next_counter)
+      * where next_counter is at most starting_counter + resync_range + 1
+      */
+      std::pair<bool,uint64_t> verify_hotp(uint32_t otp, uint64_t starting_counter, size_t resync_range = 0);
+   private:
+      std::unique_ptr<MessageAuthenticationCode> m_mac;
+      uint32_t m_digit_mod;
+   };
+
+}
+
+#endif