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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 aessiv
import (
"bytes"
"fmt"
"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 represents an AES-SIV key and function that implements RFC 5297.
type Key struct {
keyBytes secretdata.Bytes
idRequirement uint32
outputPrefix []byte
parameters *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:
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 AES-SIV key with key, idRequirement and parameters.
//
// The idRequirement is the ID requirement to be included in the output of the
// AES-SIV function. If parameters.HasIDRequirement() == false, idRequirement
// must be zero.
func NewKey(keyBytes secretdata.Bytes, idRequirement uint32, parameters *Parameters) (*Key, error) {
if parameters == nil {
return nil, fmt.Errorf("aessiv.NewKey: parameters is nil")
}
if err := validateParams(parameters); err != nil {
return nil, fmt.Errorf("aessiv.NewKey: %v", err)
}
if !parameters.HasIDRequirement() && idRequirement != 0 {
return nil, fmt.Errorf("aessiv.NewKey: idRequirement = %v and parameters.HasIDRequirement() = false, want 0", idRequirement)
}
if keyBytes.Len() != int(parameters.KeySizeInBytes()) {
return nil, fmt.Errorf("aessiv.NewKey: key.Len() = %v, want %v", keyBytes.Len(), parameters.KeySizeInBytes())
}
outputPrefix, err := calculateOutputPrefix(parameters.Variant(), idRequirement)
if err != nil {
return nil, fmt.Errorf("aessiv.NewKey: %v", err)
}
return &Key{
keyBytes: keyBytes,
idRequirement: idRequirement,
outputPrefix: outputPrefix,
parameters: parameters,
}, nil
}
// KeyBytes returns the key material.
//
// This function provides access to partial key material. See
// https://developers.google.com/tink/design/access_control#access_of_parts_of_a_key
// for more information.
func (k *Key) KeyBytes() secretdata.Bytes { return k.keyBytes }
// Parameters returns the parameters of this key.
func (k *Key) Parameters() key.Parameters { return k.parameters }
// IDRequirement returns a tuple containing a boolean that indicates whether or
// not the key requires an identifier and the key identifier. The key identifier
// will equal 0 if an identifier is not required.
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, thisIDRequired := k.IDRequirement()
thatIDRequirement, thatIDRequired := that.IDRequirement()
return ok && k.Parameters().Equal(that.Parameters()) &&
thisIDRequired == thatIDRequired &&
thisIDRequirement == thatIDRequirement &&
k.keyBytes.Equal(that.keyBytes) &&
bytes.Equal(k.outputPrefix, that.outputPrefix)
}
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