Key Management

Key Management

Guidance for selecting key types, issuing code signing certificates, integrating with HSMs/KMS, and lifecycle operations.

Key types & algorithms

• RSA — use RSA 3072 or higher for compatibility; RSA 4096 for long-lived, higher security needs.
• ECDSA — P-256 / P-384 are common; P-256 often favored for performance and size.
• Prefer algorithms supported by your target verification environment (platform tooling, package managers).

Certificates & EKU

• Request certificates with the Code Signing Extended Key Usage (EKU) set by the issuing CA.
• Maintain a certificate chain and ensure the verification path is available to consumers.
• For timestamping, rely on RFC 3161 timestamp tokens from trusted TSA providers and store the token with the signature.

Issuance patterns

• HSM-backed keys: Generate the key inside the HSM and create a CSR that references the public key. The private key never leaves the HSM.
• KMS-backed keys: Use provider IAM policies to bind key usage to the signing service and restrict operations.

Example: Generate CSR with local key (OpenSSL)

# Generate key (local/private example - prefer HSM generation in prod)
openssl genpkey -algorithm RSA -out signing.key -pkeyopt rsa_keygen_bits:3072

# Create CSR with Code Signing EKU
openssl req -new -key signing.key -subj "/CN=Acme Code Signing" -addext "keyUsage = digitalSignature" -addext "extendedKeyUsage = codeSigning" -out signing.csr

Example: SoftHSM / PKCS#11 (dev)

# Initialize and create key in SoftHSM (example)
softhsm2-util --init-token --slot 0 --label "dev-token" --so-pin 1234 --pin 1234
pkcs11-tool --module /usr/lib/softhsm/libsofthsm2.so -l --pin 1234 --keypairgen --key-type rsa:3072 --id 01 --label "signing-key"
# Extract public key to create CSR (vendor tools or pkcs11-tool export)

PKCS#11 URI example:

pkcs11:token=dev-token;id=%01;object=signing-key;type=private

Private key handling

• Never export private keys from HSMs unless the vendor supports secure wrapped backup.
• Use HSM-backed signing operations or a signing agent/proxy so that private material is never exposed to application memory in plaintext.
• Use access controls (PINs, role separation) and rotate PINs/credentials regularly.

Certificate lifecycle & rotation

• Plan certificate expiry and key rotation well ahead of expiry dates; automate renewals when possible.
• Maintain overlapping validity windows when rotating keys to avoid service downtime.
• Revoke certificates when keys are compromised and publish revocation to consumers as needed (OCSP/CRL where applicable).

Verification & timestamping

• Always verify signatures locally against the certificate chain and timestamp tokens where required.
• Timestamp tokens (RFC 3161) preserve signature validity beyond certificate expiry when included and validated.

Checklist (Key & Certificate Operations)

• Keys generated inside HSM or provider KMS
• CSR created with EKU=codeSigning and proper subject details
• Certificate chain stored and accessible for verification
• Timestamping configured if required for long-term validity
• Key rotation scheduled and tested
• Revocation & incident procedures in place

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See also: HSM Setup, Security Best Practices.