BIOS ROM Integrity Verification via Encrypted Message Digest
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Solution Overview
Problem
Existing methods for securing a computing system's BIOS struggle to balance accessibility for upgrades with protection against unauthorized tampering, as moving BIOS storage onto the microprocessor die complicates upgrades and encrypting BIOS contents degrades system performance.
Innovation Solution
A technique involving a BIOS ROM with plaintext contents and an encrypted message digest, using a symmetric key algorithm, where a tamper detector within the microprocessor compares generated and decrypted message digests to ensure integrity and allows operation only if they match, and a random number generator sets intervals for subsequent BIOS checks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BIOS storage is moved onto the microprocessor die, then protection against tampering is improved, but ease of upgrade deteriorates
Solution Approach 1:
The invention separates the BIOS storage (in external ROM) from the microprocessor die, while segmenting the protection mechanism into two parts: the BIOS contents stored externally and the cryptographic verification logic embedded in the microprocessor. This allows the BIOS to be upgraded by simply replacing the external ROM chip, while the security functionality remains integrated in the processor.
Solution Approach 2:
The invention introduces an intermediary cryptographic verification mechanism that bridges the external BIOS storage and the microprocessor. The microprocessor contains cryptographic logic to verify the integrity of externally stored BIOS without requiring the BIOS to be physically integrated, thus enabling both external storage and security verification.
2Reliability
If BIOS contents are encrypted, then protection against tampering is improved, but system performance deteriorates
Solution Approach 1:
The invention extracts only the essential verification element (message digest or hash) and stores it externally alongside the BIOS contents, rather than encrypting the entire BIOS. This allows the BIOS to be stored in plaintext for fast access, while only the small message digest requires cryptographic processing during verification.
Solution Approach 2:
The invention changes the parameter of cryptographic protection from full encryption of BIOS contents to hashing only the message digest. This parameter change reduces the computational overhead from O(n) where n is the BIOS size to O(d) where d is the small digest size, significantly improving performance while maintaining security.
3Productivity
If BIOS contents are stored as plaintext, then system performance is improved, but protection against tampering deteriorates
Solution Approach 1:
The invention creates a cryptographic copy (message digest or hash) of the BIOS contents and stores it externally. This copy serves as a tamper-evident seal that can be verified without encrypting the original BIOS, allowing the plaintext BIOS to be accessed quickly while the digest provides security verification.
Data Source
AI summary
An apparatus including a BIOS read only memory (ROM) and a tamper detector. The BIOS ROM includes BIOS contents stored as plaintext, and an encrypted message digest comprising an encrypted version of a first message digest that corresponds to the BIOS contents. The tamper detector is coupled to the BIOS ROM, and accesses the BIOS contents and the encrypted message digest upon reset of a microprocessor, and directs the microprocessor to generate a second message digest corresponding to the BIOS contents and a decrypted message digest corresponding to the encrypted message digest using the same algorithms and key that were employed to generate the first message digest and the encrypted message digest, and compares the second message digest with the decrypted message digest, and precludes the operation of the microprocessor if the second message digest and the decrypted message digest are not equal.