DKIM Message Protocol with Declared Recipients Against Replay
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Solution Overview
Problem
DomainKeys Identified Mail (DKIM) is vulnerable to replay attacks and disrupts mailing and forwarding lists, lacking effective replay protection and privacy in recipient declaration.
Innovation Solution
A message protocol that enhances DKIM by explicitly declaring all recipients, including blind carbon copy (BCC) recipients, and employs challenge requests to verify sender authenticity, while allowing header and body modifications with dual signatures to maintain authenticity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DKIM digitally signs messages to provide authenticity protection, then message authenticity is improved, but the system becomes vulnerable to replay attacks
Solution Approach 1:
The patent applies preliminary action by requiring the recipient to send a challenge request to the sender before the actual message is processed. The sender must sign this challenge request with their DKIM private key, creating a pre-verification that binds the signature to a specific communication session. This preliminary signing action prevents replay attacks because the signed challenge request contains unique identifiers that cannot be reused in subsequent messages.
Solution Approach 2:
The patent implements feedback by having the recipient verify the signed challenge request and send the verification result back to the sender. This feedback loop confirms that the sender possesses the valid DKIM private key and establishes a trusted communication channel. The feedback mechanism ensures that both parties are actively participating in the authentication process, making replay attacks ineffective.
2Reliability
If DKIM verifies sender authenticity through digital signatures, then message integrity is improved, but mailing lists and forwarding functionality are disrupted
Solution Approach 1:
The challenge request signing process occurs before the message is forwarded or added to mailing lists. This preliminary authentication establishes trust that can be carried through subsequent message modifications. The signed challenge request serves as a credential that remains valid even when the message is redistributed to multiple recipients.
Solution Approach 2:
The patent separates the authentication verification from the message delivery process. The challenge request signing and verification is a distinct preliminary step that validates the sender, while the actual message can then be freely forwarded or distributed to mailing lists. This segmentation allows message integrity to be verified once at the source, while adaptability is maintained for subsequent distribution.
Data Source
AI summary
A method for securing messages includes obtaining, at a first message server, a message for a user of a message service hosted by the first message server, the message including a header including a digital signature signed by an author of the message and a list of one or more recipients of the message. The method includes determining that a Domain Name System (DNS) TXT record associated with the message includes a delegation policy indicating that a second message server declared all intended recipients of the message. In response, the method includes determining that the digital signature by the author is valid and that the user is a declared recipient of the message. The method includes, in response to determining that the digital signature by the author is valid and the user is the declared recipient of the message, indicating the message is authentic.