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// Copyright 2024 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 aesctrhmac
import (
"bytes"
"fmt"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/secretdata"
)
// Key represents an AES-CTR-HMAC AEAD function.
type Key struct {
aesKeyBytes secretdata.Bytes
hmacKeyBytes secretdata.Bytes
idRequirement uint32
outputPrefix []byte
parameters *Parameters
}
var _ key.Key = (*Key)(nil)
// KeyOpts specifies parameters to [NewKey].
type KeyOpts struct {
AESKeyBytes, HMACKeyBytes secretdata.Bytes
IDRequirement uint32
Parameters *Parameters
}
// NewKey creates a new AES-CTR-HMAC key with key, idRequirement and parameters.
//
// The idRequirement is the ID requirement to be included in the output of the
// AES-CTR-HMAC function. If parameters.HasIDRequirement() == false, idRequirement
// must be zero.
func NewKey(params KeyOpts) (*Key, error) {
// Make sure that parameters is not nil and that is not as struct literal
// with default values.
if params.Parameters == nil || params.Parameters.AESKeySizeInBytes() == 0 {
return nil, fmt.Errorf("aesctrhmac.NewKey: invalid input params.Parameters")
}
if !params.Parameters.HasIDRequirement() && params.IDRequirement != 0 {
return nil, fmt.Errorf("aesctrhmac.NewKey: params.IDRequirement = %v and params.Parameters.HasIDRequirement() = false, want 0", params.IDRequirement)
}
if params.AESKeyBytes.Len() != int(params.Parameters.AESKeySizeInBytes()) {
return nil, fmt.Errorf("aesctrhmac.NewKey: AES key length = %v, want %v", params.AESKeyBytes.Len(), params.Parameters.AESKeySizeInBytes())
}
if params.HMACKeyBytes.Len() != int(params.Parameters.HMACKeySizeInBytes()) {
return nil, fmt.Errorf("aesctrhmac.NewKey: HMAC key length = %v, want %v", params.HMACKeyBytes.Len(), params.Parameters.HMACKeySizeInBytes())
}
outputPrefix, err := calculateOutputPrefix(params.Parameters.Variant(), params.IDRequirement)
if err != nil {
return nil, fmt.Errorf("aesctrhmac.NewKey: %v", err)
}
return &Key{
aesKeyBytes: params.AESKeyBytes,
hmacKeyBytes: params.HMACKeyBytes,
idRequirement: params.IDRequirement,
outputPrefix: outputPrefix,
parameters: params.Parameters,
}, nil
}
// AESKeyBytes 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) AESKeyBytes() secretdata.Bytes { return k.aesKeyBytes }
// HMACKeyBytes 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) HMACKeyBytes() secretdata.Bytes { return k.hmacKeyBytes }
// Parameters returns the parameters of this key.
func (k *Key) Parameters() key.Parameters { return k.parameters }
// 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, thisIDRequired := k.IDRequirement()
thatIDRequirement, thatIDRequired := that.IDRequirement()
return ok && k.Parameters().Equal(that.Parameters()) &&
thisIDRequired == thatIDRequired &&
thisIDRequirement == thatIDRequirement &&
k.aesKeyBytes.Equal(that.aesKeyBytes) &&
k.hmacKeyBytes.Equal(that.hmacKeyBytes) &&
bytes.Equal(k.outputPrefix, that.outputPrefix)
}
func createKey(p key.Parameters, idRequirement uint32) (key.Key, error) {
aesCTRHMACParams, ok := p.(*Parameters)
if !ok {
return nil, fmt.Errorf("key is of type %T; needed %T", p, (*Parameters)(nil))
}
aesKeyBytes, err := secretdata.NewBytesFromRand(uint32(aesCTRHMACParams.AESKeySizeInBytes()))
if err != nil {
return nil, err
}
macKeyBytes, err := secretdata.NewBytesFromRand(uint32(aesCTRHMACParams.HMACKeySizeInBytes()))
if err != nil {
return nil, err
}
return NewKey(KeyOpts{
AESKeyBytes: aesKeyBytes,
HMACKeyBytes: macKeyBytes,
IDRequirement: idRequirement,
Parameters: aesCTRHMACParams,
})
}
// KeyCreator returns a key creator function.
//
// It is *NOT* part of the public API.
func KeyCreator(t internalapi.Token) func(p key.Parameters, idRequirement uint32) (key.Key, error) {
return createKey
}
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