In Eclipse Jetty, the Digest authentication server-side component uses ISO-8859-1 to encode the password as bytes. This was done because the initial specification for HTTP did not specify explicitly a charset, and it was assumed to be ISO-8859-1 for historical reasons. If the password contains characters that cannot be represented in ISO-8859-1, they are silently replaced by "?". This happens with passwords that contain Chinese, Cyrillic or Greek characters, for example: "αβ123" converts to "??123". An attacker can send a request with a digest "Authorization" header crafted with a password made of only "?" characters; the server would match any password of the same length that contains non-ISO-8859-1 characters. Recent HTTP Digest "RFC-7616" (https://datatracker.ietf.org/doc/html/rfc7616) supports a "charset" parameters that defaults to UTF-8 that allows for correct encoding/decoding of passwords.