Data, data ; Jaganathan, et al. Checksum ; RC4 K3, edata. Confounder ; RC4 K3, data. Confounder ; RC4 K3, edata. Confounder, edata. Data ; if checksum! The character constant "fortybits" evolved from the time when a bit key length was all that was exportable from the United States. It is now used to recognize that the key length is of "exportable" length.
In this description, the key size is actually 56 bits. Key Strength Negotiation A Kerberos client and server can negotiate over key length if they are using mutual authentication.
If the client is unable to perform full-strength encryption, it may propose a key in the "subkey" field of the authenticator, using a weaker encryption type. The server must then either return the same key or suggest its own key in the subkey field of the AP reply message.
The key used to encrypt data is derived from the key returned by the server. If the client is able to perform strong encryption but the server is not, it may propose a subkey in the AP reply without first being sent a subkey in the authenticator. See [RFC] Section 1. These flags are passed in the checksum field of the authenticator.
Setting this flag causes an extra AP reply to be sent from the client back to the server after receiving the server's Jaganathan, et al. In particular, Windows status codes may be returned in the data field of a Kerberos error message.
This allows the client to understand a server failure more precisely. In addition, the server may return errors to the client that are normally handled at the application layer in the server, in order to let the client try to recover.
After receiving an error message, the client may attempt to resubmit an AP request. Only the first 8 octets of the checksum are used. All padding is rounded up to 1 byte. One byte is needed to say that there is 1 byte of padding. The DES-based mechanism type uses 8-byte padding. Header, Token. Security Considerations Care must be taken in implementing these encryption types because they use a stream cipher.
If a different IV is not used in each direction when using a session key, the encryption is weak. By using the sequence number as an IV, this is avoided. Strong distinguishers distinguish an RC4 keystream from randomness at the start of the stream. As mentioned before, this may be a computer object, or it could be a service account that is being used to host the resource on the network. If the attribute has no value defined, the domain controller will encrypt the ticket with RC4 to ensure compatibility.
By default, user accounts do not have a value set so unless you have manually enabled AES on them, tickets for service accounts will be encrypted with RC4. Once the computer processes that policy it will update the attribute on its own computer object. Referral Ticket encryption type — The encryption used for a referral ticket and session key is determined by the trust properties and the encryption types supported by the client. Otherwise the referral ticket will be encrypted with RC4.
By default, trusts including inter-forest trusts do not have AES support enabled. When deciding to enable AES on a trust keep in mind the client does not read the contents of the referral ticket, but it does need a common session key encryption type.
If you are considering disabling RC4 over a trust please first review KB In my role as Sr Customer Engineer I find the fear of the unknown to be the primary reason security hardening recommendations are not embraced. Moving forward with enforcing AES for Kerberos will require analysis and one of the best inputs for that assessment are events from the domain controller security log which show the encryption type Ticket Encryption Type field of issued service tickets.
Event will show the same information for issued TGTs. If you have the luxury of having centralized log collection and analysis tool, then getting a quick handle on your ticket encryption types will be achievable. Without such a solution you are facing a tough challenge. The table below maps the values in the events to the encryption type of the issued tickets. Event ID 16 can also be useful when troubling scenarios where a service ticket request failed because the account did not have an AES key.
That was a lot of information on a complex topic. Here is a quick summary to help you determine your next move. Thanks for reading.
I hope this information helps you move forward with eliminating RC4 encryption without unexcepted impacts. You can find the original article here.
I've been doing system administration since roughly and in that time I've come to realize one thing: making changes to established environments always causes a ripple effect.
Background Flash back to the late 80's Improve this answer. Steve Steve Your answer doesn't really answer this part. Short answer: no. The AES key is derived from the raw password. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
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