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Add docs and warning around the use of latest key version alias #694

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Merged
AlCutter merged 1 commit into from
Feb 3, 2026
Merged

Add docs and warning around the use of latest key version alias #694

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15 changes: 15 additions & 0 deletions cmd/tesseract/gcp/README.md
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Expand Up @@ -12,6 +12,21 @@ You can find more information about TesseraCT in general in the
[architecture design doc](/docs/architecture.md), and in TesseraCT's
[configuration guide](../).

## Keys and Secret Manager

Log private and public keys are stored as secrets in Secret Manager, and the full secret version resource
names passed to
`--signer_private_key_secret_name` and `--signer_public_key_secret_name` respectively.

> [!WARNING]
> While the `latest` version alias is supported, unless you are sure you know what you are doing, we
> strongly recommend the use of specific version IDs instead.
>
> Using `latest` will cause the log's key to be updated without warning if a new secret version is
> created. Since CT for the WebPKI currently does not support log key rotation, other than through
> retiring log shards and bringing up new ones, automatic rotation of the log key, inadvertant or
> otherwise, will therefore almost certainly result in an unplanned outage.

## Witnessing

> [!WARNING]
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7 changes: 4 additions & 3 deletions cmd/tesseract/gcp/secret_manager.go
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Expand Up @@ -74,6 +74,10 @@ func NewSecretManagerSigner(ctx context.Context, publicKeySecretName, privateKey
}
}()

if strings.HasSuffix(privateKeySecretName, "/latest") {
klog.Warning("Secret version configured to use 'latest' alias; log key will change if a newer version is created.")
}

// Public Key
var publicKey crypto.PublicKey
pemBlock, err := secretPEM(ctx, client, publicKeySecretName)
Expand Down Expand Up @@ -129,9 +133,6 @@ func secret(ctx context.Context, client *secretmanager.Client, secretName string
if err != nil {
return nil, fmt.Errorf("failed to access secret version: %w", err)
}
if resp.Name != secretName {
return nil, errors.New("request corrupted in-transit")
}
// Verify the data checksum.
crc32c := crc32.MakeTable(crc32.Castagnoli)
checksum := int64(crc32.Checksum(resp.Payload.Data, crc32c))
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