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- Thread starterLesha Pipiev
- Start dateYesterday at 12:17 PM
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Lesha Pipiev
- Yesterday at 12:17 PM
- #1
Due to there are large encrypted files we are dealing with, we can't afford to keep entire file in memory during a decryption process.
I've implemented the algorithm of chunked decryption of AES GSM encrypted file.
Code:
const ( tagSizeInBytes = 16 BufferSizeInBytes = 5 * 1024 * 1024)func DecryptFile(encryptedFile, decryptedFile *os.File, encryptedFileSize int64, dataKey, iv []byte) error { sizeOfEncryptedFileWithoutTag := encryptedFileSize - int64(tagSizeInBytes) c, err := aes.NewCipher(dataKey) if err != nil { return err } var encryptedChunk = make([]byte, BufferSizeInBytes) var lastIteration = false var offset = 0 for { nBytes, err := encryptedFile.Read(encryptedChunk) if err != nil { if err != io.EOF { fmt.Println(err) } break } if int64(offset+BufferSizeInBytes) >= sizeOfEncryptedFileWithoutTag { var endIndex = sizeOfEncryptedFileWithoutTag - int64(offset) if endIndex < 0 { endIndex = int64(nBytes) } encryptedChunk = encryptedChunk[0:endIndex] lastIteration = true } // iv is of 12 bytes size // counter has to be 16 bytes size extra := make([]byte, 4) counter := append(iv, extra[:]...) // in order to "jump" to specific offset in encrypted message, // we need to increment counter // init counter inc(counter) for i := 0; i < offset/aes.BlockSize+1; i++ { inc(counter) } var endIndex = offset + BufferSizeInBytes if endIndex > len(encryptedChunk) { endIndex = len(encryptedChunk) } encryptedBlock := encryptedChunk[0:endIndex] ctr := cipher.NewCTR(c, counter) plain := make([]byte, len(encryptedBlock)) ctr.XORKeyStream(plain, encryptedBlock) if _, err = decryptedFile.Write(plain); err != nil { fmt.Println(err) os.Exit(1) } offset += BufferSizeInBytes if lastIteration { break } } return nil}The method works fine, but there is no tag authentication check.
Is it possible to implement tag verification for chunked AES-GCM decryption?
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