Data Sheet

Ethernet Controller I210 —Interconnects
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Integrity validation of Flash updates is provided by means of a digital signature. The digital signature is
a SHA256 Hash computed over the protected content (long by 256-bits), which is then encrypted by a
2048-bits RSA encryption using an Intel private key. This digital signature is stored in what is called the
manifest in the Flash module image. Also stored in the manifest is the corresponding RSA Modulus (the
public key) and RSA Exponent parameters to be used for decrypting the digital signature.
To verify the authenticity of the digital signature, firmware must first verify that the RSA Modulus and
RSA Exponent fields in the new firmware image loaded are identical to those in the old FW image. If the
RSA Modulus and Exponent fields are the same, firmware decrypts the digital signature using the 2048-
bit RSA Modulus and Exponent fields stored in the manifest of the old firmware image to extract the
expected SHA256 Hash of content (stored hash). Firmware then performs an independent SHA256
Hash over the protected content (computed hash). If the stored hash matches the computed hash, the
digital signature is accepted, and the Flash update is applied.
Flash updates are validated prior to invalidating the old Flash configuration, such that the old Flash
configuration is still usable if the update fails to validate. After the new Flash is successfully verified, the
firmware switches to the new image.
Figure 3-8. Sign and Verify Procedures for Authenticated Flash Modules
3.3.10.1 Digital Signature Algorithm Details
As previously mentioned, the digital signature generation is a hash computation followed by an RSA
encryption. This is performed within Intel as part of the Flash update image generation process and not
performed by Intel software in the field, nor by the I210.
The algorithms used are described in the following locations:
• PKCS #1 v2.1: RSA Cryptography Standard, RSA Laboratories, June 14, 2002 -
• SHA family definition -
• SHA usage with digital signatures -
• SHA validation vectors -
Protected
Module
Contents
Digest
SHA256
Hash
Verify
CSS Header
Digital
Signature
Module’s
Manifest
2048-bits
RSA Modulus
RSA Exponent
Private key
RSA encryption
Protected
Module
Contents
Digest
SHA256
Hash
CSS Header
2048-bits
RSA Modulus
RSA Exponent
Public key
RSA decryption
= ?
Sign
New = Old ?
www.rsa.com
http://csrc.nist.gov/publications/fips/fips180-3/fips180-3_final.pdf
http://csrc.nist.gov/publications/nistpubs/800-107/NIST-SP-800-107.pdf
http://csrc.nist.gov/groups/STM/cavp/documents/shs/SHAVS.pdf