require 'openssl' require 'base64' key = 'the shared secret key here' message = 'the message to hash here' # to lowercase hexits OpenSSL:: HMAC. hexdigest

hmac = hash( (key xor opad) + hash((key xor ipad) xor message) ) So it's just some hash functions and xorring values together, nothing else. Block ciphers typically need a fixed-length key, but cryptographic hash functions "[map] data of arbitrary size to a bit string of a fixed size (a hash)". HMAC_CTX h; memcpy(h.key, KeyDataFromSomewhere, sizeof h.key) However, this is risky. It's far too easy to get the HMAC into an inconsistent state and ultimately get wrong results. Instead, when the object is declared as opaque: typedef struct hmac_ctx_st HMAC_CTX; The code above will now fail: % cat a.c #include "openssl/hmac.h" #include openssl dgst -sha256 -mac hmac -macopt hexkey:$(cat mykey.txt) -out hmac.txt /bin/ps Since we're talking about cryptography, which is hard; and OpenSSL, which doesn't always have the most easy-to-use interfaces, I would suggest also verifying everything yourself, at least twice, instead of taking my word for it. If you encountered this compiling issue - "aggregate ‘HMAC_CTX ctx’ has incomplete type and cannot be defined" etc, basically, it means you're using a higher version of openssl (>=v1.1.0). HMAC Generator / Tester Tool. Computes a Hash-based message authentication code (HMAC) using a secret key. A HMAC is a small set of data that helps authenticate the nature of message; it protects the integrity and the authenticity of the message. PHP OpenSSL functions openssl_encrypt() and openssl_decrypt() seem to use PKCS5/7 style padding for all symmetric ciphers. Upon this, you can't use them to encrypt using null byte padding or to decrypt null byte padded data. A hashed message authentication checksum (HMAC) is typically used to verify that a message has not been changed during transit. Both parties to the message must have a shared secret key. The sender combines the key and the message into a string, creates a digest of the string by using an algorithm such as SHA-1 or MD5, and transmits the message

RFC 2104 HMAC February 1997 3.Keys The key for HMAC can be of any length (keys longer than B bytes are first hashed using H). However, less than L bytes is strongly discouraged as it would decrease the security strength of the function.

OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. It is also a general-purpose cryptography library. OpenSSL is widely used by developers and can be found in a huge number of products. OpenSSL 1.1.1 was released on 11 September 2018.

Using openssl to generate HMAC using a binary key If you want to do a quick command-line generation of a HMAC, then the openssl command is useful.

Returns the authentication code as a hex-encoded string. The digest parameter specifies the digest algorithm to use. This may be a String representing the algorithm name or an instance of OpenSSL::Digest. HMAC-based Extract-and-Expand Key Derivation Function (HKDF) as specified in RFC 5869. New in ::OpenSSL 1.1.0. Parameters ikm. The input keying material. salt. The salt. info. The context and application specific information. length. The output length in octets. Must be <= 255 * HashLen, where HashLen is the length of the hash function output Online HMAC hash generator: HMAC-MD5, HMAC-SHA. A keyed-hash message authentication code (HMAC) uses a cryptographic hash function (MD5, SHA-1, SHA-512 …) and a secret cryptographic key to verify both the data integrity and the authentication of a message. require 'openssl' require 'base64' key = 'the shared secret key here' message = 'the message to hash here' # to lowercase hexits OpenSSL:: HMAC. hexdigest I realise this isn't exactly what you're asking for, but there's no point in reinventing the wheel and writing a bash version. You can simply use the openssl command to generate the hash within your script. [me@home] echo -n "value" | openssl dgst -sha1 -hmac "key" 57443a4c052350a44638835d64fd66822f813319