Encryption at Rest

A field tagged mfx:"encrypted" is automatically encrypted before it reaches the database and decrypted on read. The plaintext never appears in the table; the column stores a self-describing envelope. This page covers the full subsystem: the tag, the key provider interface, the storage format, unique-constraint handling, and key rotation.

Declaring an encrypted field

type Patient struct {
    maniflex.BaseModel
    Name string `json:"name" mfx:"required,filterable,sortable"`
    SSN  string `json:"ssn"  mfx:"encrypted,key:patient-pii"`
}

The column’s Go and DB types remain string. Storage is the prefix enc: followed by a base64-encoded binary envelope:

enc:Aa1z...   (envelope bytes embed the keyID)

The enc: prefix lets the framework distinguish ciphertext from any legacy plaintext that may exist in the column — useful for incremental migration of an existing table.

What encryption costs you

The trade-offs are deliberate and worth being explicit about:

• No filtering. A WHERE ssn = ? would have to match an envelope that includes a random nonce. Encrypted fields cannot be filterable.
• No sorting. Same reason. Encrypted fields cannot be sortable.
• Uniqueness via HMAC. A mfx:"encrypted,unique" field gets a companion {field}_hmac TEXT UNIQUE column. See the next section.
• The KeyProvider is required. Reads degrade to returning the raw stored ciphertext; writes are rejected with 500 ENCRYPTION_NOT_CONFIGURED until a provider is configured.

For columns that need to be queryable but contain sensitive data, store a non-sensitive lookup key (a hashed identifier) in a separate field and encrypt only the payload.

Configuring a KeyProvider

maniflex.Config.KeyProvider must be set before any model with encrypted fields is exercised. Two implementations ship in pkg/encryption, both constructed as plain struct literals.

EnvKeyProvider — keys from environment variables

import "github.com/xaleel/maniflex/pkg/encryption"

server := maniflex.New(maniflex.Config{
    KeyProvider: &encryption.EnvKeyProvider{Prefix: "MYAPP_KEY"},
    // ...
})

The env var name for a given keyID is derived as {Prefix}_{KEYID_UPPER}, with hyphens replaced by underscores and the result uppercased:

Each variable holds a base64-encoded 32-byte (256-bit) AES key. Generate one with:

openssl rand -base64 32

The provider accepts either standard or URL-safe base64.

VaultKeyProvider — HashiCorp Vault Transit

server := maniflex.New(maniflex.Config{
    KeyProvider: &encryption.VaultKeyProvider{
        Address: "https://vault.example.com",
        Token:   os.Getenv("VAULT_TOKEN"),
        Mount:   "transit",            // optional, default "transit"
        // Client: customHTTPClient,    // optional, defaults to http.DefaultClient
    },
})

keyID maps to a Vault Transit key name; the plaintext is sent to /v1/{mount}/encrypt/{keyID} and Vault returns its own vault:v1:... ciphertext, which the provider embeds in the envelope. A Vault key rotation is transparent — Vault decrypts ciphertexts encrypted with any prior version of the key automatically.

The shipped provider uses a static token. For production, wrap it with a refresher that obtains a fresh token from AppRole, Kubernetes auth, or JWT auth before each operation.

A custom backend implements the maniflex.KeyProvider interface:

type KeyProvider interface {
    Encrypt(ctx context.Context, keyID string, plaintext []byte) ([]byte, error)
    Decrypt(ctx context.Context, envelope []byte) ([]byte, error)
    KeyIDOf(envelope []byte) (string, error)
    HMAC(ctx context.Context, keyID string, data []byte) ([]byte, error)
}

Encrypt returns a self-describing binary envelope that embeds the keyID. Decrypt reads the keyID from the envelope, so callers don’t supply it. HMAC produces a deterministic keyed digest used for unique indexes.

Unique encrypted fields

A normal UNIQUE constraint on an envelope is useless — each envelope contains a random nonce, so two encryptions of the same plaintext are different ciphertexts. The framework solves this with an HMAC companion column.

Email string `json:"email" mfx:"encrypted,unique"`

AutoMigrate emits two columns:

On every write, the DB step calls KeyProvider.HMAC(ctx, keyID, plaintext) and stores the result in the companion. The HMAC is deterministic for a given (key, plaintext) pair, so the database can enforce uniqueness without ever seeing the plaintext.

Reads strip the HMAC column from responses automatically; clients see only the decrypted plaintext on email and never the digest.

When the unique check fires, the adapter returns *maniflex.ErrConstraint and the DB step converts it to 409 CONFLICT — same path as any other unique violation.

Per-domain keys

The key:NAME sub-option routes a field to a specific key identifier:

type Record struct {
    maniflex.BaseModel
    PaymentToken string `json:"payment_token" mfx:"encrypted,key:billing"`
    MedicalNote  string `json:"medical_note"  mfx:"encrypted,key:medical"`
}

A KeyProvider that backs different keys with different secrets (or a Vault transit mount) lets you scope access by domain — the billing team holds the billing key; medical staff hold the medical key; the application process holds both. Rotating one does not affect the other.

When key: is omitted, the framework uses the keyID "default". Either configure a key under that name or always tag with an explicit key.

Decryption on the read path

The DB step runs the decryption pass after every read:

• For list and read operations, decryptFields replaces every enc:<base64> value with the decrypted plaintext.
• HMAC companion columns are always stripped from the response.
• Values that do not have the enc: prefix are left as-is — important for gradual adoption: enable encryption on a column whose existing rows are plaintext, and only new writes get encrypted.

If KeyProvider is nil but a model has encrypted fields, reads return the raw stored ciphertext (so the application still functions in some read-only sense), but writes are refused. Configuring a provider is the only way to write encrypted columns.

Key rotation

maniflex.RotateEncryptionKey(ctx, server, modelName, oldKeyID, newKeyID) re-encrypts every row of a model whose envelopes were encrypted with oldKeyID:

n, err := maniflex.RotateEncryptionKey(ctx, server, "Patient", "v1", "v2")
if err != nil {
    log.Fatal(err)
}
log.Printf("re-encrypted %d rows", n)

The function pages through the table 100 rows at a time, decrypts each value with the old key, re-encrypts with the new key, and updates the HMAC companion for any unique encrypted fields. Both keys must remain available in the KeyProvider until the rotation completes — partial rotations leave the table with a mix of old-key and new-key envelopes until you finish.

The operation is not atomic across all rows. On failure, run it again — it skips envelopes whose keyID already matches newKeyID, so a partial rotation is safe to resume.

For large tables, run the rotation as a background job rather than at startup. Each row is a separate UPDATE, so the operation is bound by the database’s write throughput.

What an envelope looks like

The exact envelope format is the KeyProvider’s concern. The two shipped providers use slightly different layouts, but both put a self-describing header in front of the ciphertext so KeyIDOf can extract the keyID without decrypting.

EnvKeyProvider — AES-256-GCM with an inline nonce:

[ version:1 ][ keyIDLen:2 (BE) ][ keyID:N ][ nonce:12 ][ gcmCiphertext+tag:M ]

VaultKeyProvider — Vault returns a vault:v1:... ciphertext that embeds its own versioning, so the envelope carries no nonce:

[ version:1 ][ keyIDLen:2 (BE) ][ keyID:N ][ vaultCiphertext:M ]

In both cases version is 0x01 and the keyID length is a 16-bit big-endian integer. The framework stores the binary envelope as the string enc:<base64> in the column.

Encrypt produces the blob; Decrypt parses the header to recover the keyID, then routes to the right key. KeyIDOf reads the keyID without decrypting — useful for audit logging and for the rotation loop above.

A custom provider need not follow either format; the framework only cares that Encrypt and Decrypt are inverses and that KeyIDOf works on the output of Encrypt.

Compatibility with other features

Operational checklist

• Set Config.KeyProvider before any encrypted-field model is registered.
• Back keys with a secret store (env vars from a vault, HashiCorp Vault Transit, AWS KMS). Never commit a key to source control.
• For staged rollout, deploy the schema (email_hmac column) before the application change that starts encrypting — and the application change before the migration that backfills existing rows.
• Keep both keys active throughout a rotation; remove the old key only after RotateEncryptionKey has reported every row migrated.
• Treat KeyIDOf(envelope) as the source of truth for “which key encrypted this row” — useful for auditing the rotation.