Sequence Number Encryption Key for 3G Network Authentication
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Solution Overview
Problem
The existing 3G AKA protocol is vulnerable to attacks where an attacker can learn information about the sequence number (SQN) during resynchronization, as the same Anonymity Key (AK*) is used when sending the same authentication vector twice, potentially revealing SQN information.
Innovation Solution
A method using a block cipher encryption function with a sequence number encryption key greater than 48 bits to encrypt the previously received sequence number, ensuring the encrypted sequence number has the same number of bits as the original, thereby preventing information revelation to attackers, even if the same sequence number is sent twice.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same Anonymity Key (AK*) is used to mask the sequence number (SQN) when sending the same authentication vector twice, then the protocol maintains consistency and simplicity, but attackers can learn information about the SQN by comparing the masked values
Solution Approach 1:
The patent changes the parameter of the masking key from a fixed Anonymity Key (AK*) to a variable key that incorporates a random component (nonce) generated for each authentication vector. This ensures that even when the same SQN is masked multiple times, different keys are used, preventing attackers from learning SQN information through comparison while maintaining protocol structure
Solution Approach 2:
The patent introduces a nonce as an intermediary element between the SQN and the masking operation. This nonce acts as a one-time pad that is combined with the SQN before masking with AK*, ensuring that each masking operation is unique and prevents cryptographic analysis attacks
2Reliability
If a longer encryption key is used to encrypt the sequence number, then security against attacks is improved, but the key length is increased beyond the standard 48 bits
Solution Approach 1:
The patent increases the security dimension by extending the key length from 48 bits to 128 bits, moving to a higher security dimension that provides stronger cryptographic protection against brute-force and analytical attacks, while maintaining compatibility with existing protocol structures through format-preserving encryption
3Reliability
If the encrypted sequence number has a different number of bits than the original, then stronger encryption can be used, but existing protocols and interfaces are impacted
Solution Approach 1:
The patent applies format-preserving encryption that changes the internal encryption parameters to use a 128-bit key while maintaining the output format as 48 bits, matching the original SQN bit length. This allows stronger encryption without impacting existing protocols and interfaces
Solution Approach 2:
The patent creates a cryptographic copy of the SQN that preserves the exact same bit length and format, allowing the encrypted value to replace the original SQN in existing protocol structures without requiring any interface or protocol modifications
Data Source
AI summary
A processing module for a communication device comprises memory for storing a key; and one or more processing elements coupled to the memory. The one or more processing elements are configured to: receive a current sequence number and a random number provided by a network entity; determine whether a value of the current sequence number is within a range determined by reference to a value of a previously received sequence number stored in the memory. When the value of the current sequence number is not within the range determined by reference to the value of the previously received sequence number, the one or more processing elements are configured to: generate a sequence number encryption key derived from the random number and the key stored in the memory, the sequence number encryption key having a length greater than 48 bits; encrypt using a block cipher encryption function, the previously received sequence number with the sequence number encryption key to provide an encrypted sequence number, wherein the block cipher encryption function is configured to generate the encrypted sequence number having the same number of bits as the previously received sequence number; provide the encrypted sequence number for sending in a response message to the network entity. A communication device, a communication system and a method are also disclosed.