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// Copyright 2025 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package hmac
import (
"bytes"
"fmt"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/internal/outputprefix"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/secretdata"
)
// Key is an HMAC key.
type Key struct {
keyBytes secretdata.Bytes
idRequirement uint32
outputPrefix []byte
params *Parameters
}
var _ key.Key = (*Key)(nil)
// calculateOutputPrefix calculates the output prefix from keyID.
func calculateOutputPrefix(variant Variant, keyID uint32) ([]byte, error) {
switch variant {
case VariantTink:
return outputprefix.Tink(keyID), nil
case VariantCrunchy, VariantLegacy:
return outputprefix.Legacy(keyID), nil
case VariantNoPrefix:
return nil, nil
default:
return nil, fmt.Errorf("invalid output prefix variant: %v", variant)
}
}
// NewKey creates a new HMAC key.
func NewKey(keyBytes secretdata.Bytes, params *Parameters, idRequirement uint32) (*Key, error) {
if keyBytes.Len() != params.KeySizeInBytes() {
return nil, fmt.Errorf("hmac.NewKey: invalid key size; want %d, got %d", keyBytes.Len(), params.KeySizeInBytes())
}
if params.Variant() == VariantNoPrefix && idRequirement != 0 {
return nil, fmt.Errorf("hmac.NewKey: key ID must be zero for VariantNoPrefix")
}
outputPrefix, err := calculateOutputPrefix(params.Variant(), idRequirement)
if err != nil {
return nil, fmt.Errorf("hmac.NewKey: %v", err)
}
return &Key{
keyBytes: keyBytes,
idRequirement: idRequirement,
outputPrefix: outputPrefix,
params: params,
}, nil
}
// KeyBytes returns the key bytes.
func (k *Key) KeyBytes() secretdata.Bytes { return k.keyBytes }
// Parameters returns the parameters of this key.
func (k *Key) Parameters() key.Parameters { return k.params }
// IDRequirement returns required to indicate if this key requires an
// identifier. If it does, id will contain that identifier.
func (k *Key) IDRequirement() (uint32, bool) {
return k.idRequirement, k.Parameters().HasIDRequirement()
}
// OutputPrefix returns the output prefix.
func (k *Key) OutputPrefix() []byte { return bytes.Clone(k.outputPrefix) }
// Equal returns whether this key object is equal to other.
func (k *Key) Equal(other key.Key) bool {
that, ok := other.(*Key)
thisIDRequirement, _ := k.IDRequirement()
thatIDRequirement, _ := that.IDRequirement()
return ok && k.Parameters().Equal(that.Parameters()) &&
thisIDRequirement == thatIDRequirement &&
k.keyBytes.Equal(that.keyBytes)
}
func primitiveConstructor(k key.Key) (any, error) {
that, ok := k.(*Key)
if !ok {
return nil, fmt.Errorf("key is of type %T, want %T", k, (*Key)(nil))
}
return NewMAC(that, internalapi.Token{})
}
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