SRP

SRP is a password-authenticated key exchange protocol that lets a client prove knowledge of a password to a server and derive a strong session key, without ever sending the password or anything usable in an offline dictionary attack by an eavesdropper. The server stores a verifier rather than the password itself, limiting damage from database theft. Standardized in RFC 2945, SRP saw adoption in products like Apple iCloud and 1Password, though newer PAKE designs such as OPAQUE are now preferred for new systems.