Implementing TOTP in Java: A Simple Example
TOTP (Time-based One-Time Password) is commonly used for two-factor authentication. This implementation demonstrates how to generate TOTP using the HMAC algorithm with SHA1, SHA256, or SHA512. Key Concepts: HMAC (Hash-based Message Authentication Code) : A cryptographic algorithm that uses a secret key and a hash function to ensure data integrity. TOTP : A method for generating one-time passwords based on the current time, making it time-sensitive. Code Breakdown: HMAC Calculation : hmac_sha() : Computes HMAC using the given algorithm ( HmacSHA1 , HmacSHA256 , or HmacSHA512 ). Example : byte [] hmacResult = hmac_sha( "HmacSHA1" , key, message); 2. Hex to Byte Conversion : hexStr2Bytes() : Converts a hexadecimal string to a byte array for processing. Example : byte [] bytes = hexStr2Bytes( "1234567890ABCDEF" ); 3. TOTP Generation : generateTOTP() : Generates a TOTP based on the key, time, and the desired length of the OTP. Example : String otp = g...