Kerberos Keys and Encryption Types

Each account has several long-term Kerberos keys, all made from its password. A user's AES256 and AES128 keys are salted with the realm in capitals and the user name (CORP.EXAMPLEdana for dana), and the RC4 key is the NT hash itself, with no salt. A computer account has the same set, made from the password Windows sets and changes for it, with a salt built from its host name.

Every encrypted part of a message names its encryption type (etype), and the client lists the types it can use, strongest first. The DC seals each ticket in a type the target account's msDS-SupportedEncryptionTypes allows, with a session key in a type both sides allow. Where that attribute is empty, the DC assumes a domain default, which the 2026 updates changed.

Since the January 2025 updates (Windows Server 2016 and later), events 4768 and 4769 in the Security log also show what each side supports, which keys exist and which type the session key used. In 4768, Ticket Encryption Type describes the TGT itself, which the krbtgt key seals, so RC4 in a TGT request shows in Pre-Authentication EncryptionType and Session Encryption Type instead.

MSDS-SupportedEncryptionTypes in these events is a processed value, so Windows Server 2022 and earlier always list DES and RC4 there, while Windows Server 2025 lists only AES and stronger. Available Keys always lists RC4, and an account whose password was last set before the domain supported AES has no AES keys until its password is reset. Read the fields together before calling RC4 an attack.

Domain controllers updated since January 2026 write Kdcsvc events 201 to 209 to the System log when a service ticket request still needs RC4, or when the DC's own default allows it (KB5073381). Since April 2026 they assume only AES for accounts whose msDS-SupportedEncryptionTypes is empty, and the July 2026 updates removed the temporary rollback setting. RC4 service tickets now survive only where the service's account, or an explicit default set on the DC, still allows RC4, and Windows Server 2025 domain controllers issue no RC4 TGTs at all.