Cryptography usage

Encryption

destination email address is encrypted with AES-128 (CTR mode);
ensure destination address privacy;
avoid spam from plaintext address in HTML pages.

Authentication

destination email address and redirection domain name are sealed with HMAC (SHA-256);
ensure parameters integrity;
avoid insecure redirection.

Note that if a redirection URL is not provided (no HERMOD_FIELDS_REDIRECT field), referrer will be use and its domain checked againts insecure redirection.

Endpoint format

Endpoint URL contains cryptographic parameter and messages: /<Cipher IV>/<Ciphered destination email address>/<MAC>