Bring Your Own Key (BYOK)

BYOK provides non-repudiation: it proves that a specific organization signed the analysis log. Use BYOK for regulatory or compliance scenarios where:

• Your organization controls the private key
• The private key never leaves your secure infrastructure
• You share only the public key with auditors
• No one outside your organization can forge signatures

When BYOK is configured, log files are dual-signed: the embedded key provides software attestation, and your BYOK key provides non-repudiation.

Generating an Ed25519 key pair

Option 1: OpenSSL (Linux / macOS)

# Generate private key in PEM format
openssl genpkey -algorithm Ed25519 -out private.pem

# Convert to DER (PKCS8) format (required by MTC Skopos)
openssl pkcs8 -topk8 -nocrypt -in private.pem -outform DER -out private.key

# Extract public key in DER format
openssl pkey -in private.pem -pubout -outform DER -out public_full.der

# Extract raw 32-byte public key (skip the 12-byte DER header)
tail -c 32 public_full.der > public.key

# Clean up intermediate files
rm private.pem public_full.der

Option 2: OpenSSL (Windows)

OpenSSL can be installed via Win32/Win64 OpenSSL or via winget install ShiningLight.OpenSSL.

# Generate private key in PEM format
openssl genpkey -algorithm Ed25519 -out private.pem

# Convert to DER (PKCS8) format (required by MTC Skopos)
openssl pkcs8 -topk8 -nocrypt -in private.pem -outform DER -out private.key

# Extract public key in DER format
openssl pkey -in private.pem -pubout -outform DER -out public_full.der

# Extract raw 32-byte public key (skip the 12-byte DER header)
$bytes = [System.IO.File]::ReadAllBytes("public_full.der")
[System.IO.File]::WriteAllBytes("public.key", $bytes[($bytes.Length - 32)..($bytes.Length - 1)])

# Clean up intermediate files
Remove-Item private.pem, public_full.der

Option 3: Python (all platforms)

pip install cryptography

from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
from cryptography.hazmat.primitives.serialization import (
    Encoding, PrivateFormat, NoEncryption, PublicFormat
)

private_key = Ed25519PrivateKey.generate()

# Save private key (PKCS8 DER)
with open("private.key", "wb") as f:
    f.write(private_key.private_bytes(Encoding.DER, PrivateFormat.PKCS8, NoEncryption()))

# Save raw 32-byte public key
with open("public.key", "wb") as f:
    f.write(private_key.public_key().public_bytes(Encoding.Raw, PublicFormat.Raw))

Configuring BYOK in MTC Skopos

1. Open Settings in the application
2. Expand the Log Signing (BYOK — Non-Repudiation) section
3. Set Private key path to your private.key file (PKCS8 DER format)
4. Set Public key path to your public.key file (raw 32-byte Ed25519 public key)
5. The application will use your keys immediately for non-repudiation signing on all subsequent analyses

Key storage recommendations

Environment	Recommendation
Minimal	Store on an encrypted disk partition with restricted file permissions (chmod 600 private.key)
Recommended	Store on a dedicated secure server or vault (e.g., HashiCorp Vault, AWS KMS)
High security	Use a Hardware Security Module (HSM) or secure enclave

General guidelines:

• Never share the private key via email, chat, or unencrypted channels
• Never commit the private key to version control
• Keep backups of the private key in a separate secure location
• Rotate keys periodically (e.g., annually). Old signatures remain verifiable
• Share only the public key (public.key) with auditors

Windows-specific key protection

Restrict file access to your user account only:

$acl = Get-Acl "private.key"
$acl.SetAccessRuleProtection($true, $false)
$acl.Access | ForEach-Object { $acl.RemoveAccessRule($_) } | Out-Null
$rule = New-Object System.Security.AccessControl.FileSystemAccessRule(
    [System.Security.Principal.WindowsIdentity]::GetCurrent().Name,
    "Read", "Allow")
$acl.AddAccessRule($rule)
Set-Acl "private.key" $acl

For disk-level encryption, enable BitLocker on the partition where the key is stored.

Sharing the public key with auditors

Provide auditors with:

1. The public.key file (32 bytes, safe to share)
2. The independent verification instructions
3. The key ID (shown in the __signature__.non_repudiation_signature.key_id field of signed log files)