Truncated MAC for Short Message Authentication
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Solution Overview
Problem
Existing message authentication methods for IoT devices face challenges in providing strong security for short messages without incurring significant overhead, as adding a full Message Authentication Code (MAC) like HMAC-SHA256 increases message size, while reducing MAC size compromises security, and concatenating messages for longer protection delays processing in time-sensitive systems.
Innovation Solution
A method where the transmitter uses bits from earlier messages as input for the MAC computation of subsequent messages, truncating the result to produce a truncated MAC, which increases confidence in earlier message integrity and reduces overhead by allowing earlier messages to have significant integrity protection without full MAC length, maintaining consistent message size across all messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a full MAC like HMAC-SHA256 is added to protect short messages, then security is improved, but message overhead increases significantly
Solution Approach 1:
The protection mechanism is segmented into two parts: (1) a truncated MAC appended to each individual message for basic protection, and (2) a batch MAC computed over concatenated messages for enhanced protection. This segmentation allows the system to provide both immediate per-message verification and cumulative batch verification, resolving the contradiction by offering multiple levels of protection with different overhead costs.
Solution Approach 2:
The patent applies partial action by using a truncated MAC (only N bits instead of full 256 bits) for individual message protection, which provides sufficient protection for short messages while minimizing overhead. The excessive action comes in the form of batch processing where multiple messages are concatenated and protected with a single MAC, providing stronger protection than individual truncation alone without proportionally increasing per-message overhead.
2Quantity of substance
If MAC size is reduced to decrease overhead, then message size is reduced, but security protection weakens
Solution Approach 1:
The patent merges individual message protection with batch message protection. The truncated MAC on each message provides immediate protection, while the batch MAC computed over concatenated messages provides cumulative protection. An attacker must successfully forge multiple truncated MACs in sequence to compromise the batch MAC, effectively providing strong security protection even with small individual MAC sizes.
Solution Approach 2:
The batch MAC mechanism creates continuity of protection across multiple messages. Instead of treating each message independently, the system continuously accumulates messages and applies MAC protection over the concatenated sequence, ensuring that protection is maintained throughout the message stream without gaps, thereby strengthening overall security despite individual MAC truncation.
3Reliability
If multiple messages are concatenated for longer MAC protection, then security is improved, but processing time increases
Solution Approach 1:
The system performs preliminary action by computing and appending a truncated MAC to each message immediately upon generation, without waiting for batch completion. This allows immediate verification of individual messages while the batch MAC is being computed in the background, reducing processing delay for time-sensitive applications while still providing the security benefits of batch processing.
Solution Approach 2:
The patent implements a dynamic protection scheme where the effective security level adapts based on the number of messages in the batch. As more messages are concatenated, the security strength increases progressively. This dynamic approach allows the system to provide adequate protection even with small batches, reducing processing time, while still offering the option for stronger protection with larger batches when time permits.
Data Source
AI summary
This application relates to devices and methods of authenticating messages exchanged over a network between a transmitter and a receiver. The transmitter generates a truncated MAC code by selecting predetermined bits from a message authentication code (MAC) computed over a concatenation of a part of the message with a part of a previously transmitted message. The transmitter appends the truncated MAC code to the message for transmission. The receiver receives a previously transmitted message, the currently transmitted message, and the truncated MAC code, and generates an expected truncated MAC code by selecting predetermined bits from a message authentication code (MAC) computed over a concatenation of the part of the message with the previously transmitted message. The receiver authenticates the message and the previously transmitted message if the truncated MAC code as received is identical to the expected truncated MAC code.