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Improve the performance of AES-CTR-HMAC by avoiding unnecessary alloc…
…ations and copies. PiperOrigin-RevId: 705911944 Change-Id: I3a6a2deb8ae12f89454e95bbb9526f10fdce74da
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,108 @@ | ||
| // 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 aead | ||
|
|
||
| import ( | ||
| "crypto/aes" | ||
| "crypto/cipher" | ||
| "fmt" | ||
|
|
||
| "github.com/tink-crypto/tink-go/v2/subtle/random" | ||
| ) | ||
|
|
||
| const ( | ||
| aesCTRMinIVSize = 12 | ||
| ) | ||
|
|
||
| // AESCTR is an implementation of IndCpa Interface. | ||
| type AESCTR struct { | ||
| key []byte | ||
| ivSize int | ||
| } | ||
|
|
||
| // NewAESCTR returns an instance of [AESCTR] unauthenticated encryption. | ||
| func NewAESCTR(key []byte, ivSize int) (*AESCTR, error) { | ||
| keySize := uint32(len(key)) | ||
| if err := ValidateAESKeySize(keySize); err != nil { | ||
| return nil, fmt.Errorf("aes_ctr: %s", err) | ||
| } | ||
| if ivSize < aesCTRMinIVSize || ivSize > aes.BlockSize { | ||
| return nil, fmt.Errorf("aes_ctr: invalid IV size: %d", ivSize) | ||
| } | ||
| return &AESCTR{key: key, ivSize: ivSize}, nil | ||
| } | ||
|
|
||
| // Encrypt encrypts plaintext using AES in CTR mode. | ||
| func (a *AESCTR) Encrypt(dst, plaintext []byte) ([]byte, error) { | ||
| if len(plaintext) > maxInt-a.ivSize { | ||
| return nil, fmt.Errorf("aes_ctr: plaintext too long") | ||
| } | ||
| ctSize := len(plaintext) + a.ivSize | ||
| if len(dst) == 0 { | ||
| dst = make([]byte, ctSize) | ||
| } | ||
| if len(dst) < ctSize { | ||
| return nil, fmt.Errorf("aes_ctr: destination buffer too small (%d vs %d)", len(dst), ctSize) | ||
| } | ||
|
|
||
| iv := random.GetRandomBytes(uint32(a.ivSize)) | ||
| stream, err := newCipher(a.key, iv) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| if n := copy(dst, iv); n != a.ivSize { | ||
| return nil, fmt.Errorf("aes_ctr: failed to copy IV (copied %d/%d bytes)", n, a.ivSize) | ||
| } | ||
| stream.XORKeyStream(dst[a.ivSize:], plaintext) | ||
| return dst, nil | ||
| } | ||
|
|
||
| // Decrypt decrypts ciphertext in the format (prefix || iv || ciphertext). | ||
| func (a *AESCTR) Decrypt(dst, ciphertext []byte) ([]byte, error) { | ||
| if len(ciphertext) < a.ivSize { | ||
| return nil, fmt.Errorf("aes_ctr: ciphertext too short") | ||
| } | ||
| ptSize := len(ciphertext) - a.ivSize | ||
| if len(dst) == 0 { | ||
| dst = make([]byte, ptSize) | ||
| } | ||
| if len(dst) < ptSize { | ||
| return nil, fmt.Errorf("aes_ctr: destination buffer too small (%d vs %d)", len(dst), ptSize) | ||
| } | ||
| stream, err := newCipher(a.key, ciphertext[:a.ivSize]) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| stream.XORKeyStream(dst, ciphertext[a.ivSize:]) | ||
| return dst, nil | ||
| } | ||
|
|
||
| func newCipher(key, iv []byte) (cipher.Stream, error) { | ||
| block, err := aes.NewCipher(key) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("aes_ctr: failed to create block cipher, error: %v", err) | ||
| } | ||
|
|
||
| // If the IV is less than BlockSize bytes we need to pad it with zeros | ||
| // otherwise NewCTR will panic. | ||
| if len(iv) < aes.BlockSize { | ||
| paddedIV := make([]byte, aes.BlockSize) | ||
| if n := copy(paddedIV, iv); n != len(iv) { | ||
| return nil, fmt.Errorf("aes_ctr: failed to pad IV") | ||
| } | ||
| iv = paddedIV | ||
| } | ||
| return cipher.NewCTR(block, iv), nil | ||
| } |
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