A binary encoding used by ASN.1.

Also a notorious source of bugs—though this is because dinguses hand write the parsers instead of using parser generators.

• Let's Encrypt article
• DER Encoding, a restricted subset
• Notes on BER from LDAP code
• More notes on BER

Indefinite lengths

• A length of 0x80 means indefinite length; the result is the concatenation of objects until 0x00 signals a break.
• Indefinite lengths can be nested. ex. adding an indefinite string to an indefinite string. Need a parse stack for correct behavior...