HSM Flow with Both Authentication and Encryption - HSM Flow with Both Authentication and Encryption - 2026.1 English - UG1283

Stage 0: Encrypt and authenticate the plain bitstream with dummy key. Add the keylife parameter if keyrolling is required.

You can provide the .nky file, or Bootgen can generate .nky file that contains the keys for encryption. Bootgen does not support obfuscated AES key generation. The keylife parameter is necessary for the keyrolling feature.

the_ROM_image:

{

[aeskeyfile] encrypt.nky

[sskfile] dummykey.pem

[encryption=aes, authentication=rsa,keylife =32] plain-system.bit

}

bootgen -arch fpga -image stage0.bif -w -o auth-encrypt-system.bit -log info

After this step, the .nky file is generated if encryption is enabled. This file contains all the keys.

For FPGA encryption flows, the AES and HMAC key values used by BitGen, Bootgen, or Vivado write_bitstream must be generated from a high-quality entropy source for fielded systems and then provided to the tools.

Stage 1: Generate hashes

See the following code for an example.

the_ROM_image:

{

[authentication=rsa] auth-encrypt-system.bit

}

 

bootgen -arch fpga -image stage1.bif -generate_hashes -log info

Stage 2: Sign the hash HSM

Here, OpenSSL is used for demonstration.

openssl rsautl -sign -inkey rsaPrivKeyInfo.pem -in auth-encrypt-system.sha384 > auth-encrypt-system.sha384.sig

You can use the HSM server to sign the hashes. For SSI technology devices, generate the signatures for each super logic region (SLR). The following example shows the code to generate the signatures for a device with four SLRs.

openssl rsautl -sign -inkey rsaPrivKeyInfo.pem -in auth-encrypt-system.0.sha384 > auth-encrypt-system.0.sha384.sig

openssl rsautl -sign -inkey rsaPrivKeyInfo.pem -in auth-encrypt-system.1.sha384 > auth-encrypt-system.1.sha384.sig

openssl rsautl -sign -inkey rsaPrivKeyInfo.pem -in auth-encrypt-system.2.sha384 > auth-encrypt-system.2.sha384.sig

openssl rsautl -sign -inkey rsaPrivKeyInfo.pem -in auth-encrypt-system.3.sha384 > auth-encrypt-system.3.sha384.sig

Stage 3: Update the RSA certificate with the actual signature

See the following code for an example.

the_ROM_image:

{

[spkfile] rsaPubKeyInfo.pem

[authentication=rsa, presign=auth-encrypt-system.sha384.sig] auth-encrypt-system.bit

}

Command:bootgen -arch fpga -image stage3.bif -w -o rsa_encrypt.bit -log info