diff options
| -rw-r--r-- | internal/contentenc/content.go | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/internal/contentenc/content.go b/internal/contentenc/content.go index e841ad0..f48080f 100644 --- a/internal/contentenc/content.go +++ b/internal/contentenc/content.go @@ -121,6 +121,22 @@ func (be *ContentEnc) DecryptBlocks(ciphertext []byte, firstBlockNo uint64, file return pBuf.Bytes(), err } +// concatAD concatenates the block number and the file ID to a byte blob +// that can be passed to AES-GCM as associated data (AD). +// Result is: aData = blockNo.bigEndian + fileID. +func concatAD(blockNo uint64, fileID []byte) (aData []byte) { + if fileID != nil && len(fileID) != headerIDLen { + // fileID is nil when decrypting the master key from the config file + log.Panicf("wrong fileID length: %d", len(fileID)) + } + const lenUint64 = 8 + // Preallocate space to save an allocation in append() + aData = make([]byte, lenUint64, lenUint64+headerIDLen) + binary.BigEndian.PutUint64(aData, blockNo) + aData = append(aData, fileID...) + return aData +} + // DecryptBlock - Verify and decrypt GCM block // // Corner case: A full-sized block of all-zero ciphertext bytes is translated @@ -157,9 +173,7 @@ func (be *ContentEnc) DecryptBlock(ciphertext []byte, blockNo uint64, fileID []b // Decrypt plaintext := be.pBlockPool.Get() plaintext = plaintext[:0] - aData := make([]byte, 8) - aData = append(aData, fileID...) - binary.BigEndian.PutUint64(aData, blockNo) + aData := concatAD(blockNo, fileID) plaintext, err := be.cryptoCore.AEADCipher.Open(plaintext, nonce, ciphertext, aData) if err != nil { @@ -257,9 +271,7 @@ func (be *ContentEnc) doEncryptBlock(plaintext []byte, blockNo uint64, fileID [] log.Panic("wrong nonce length") } // Block is authenticated with block number and file ID - aData := make([]byte, 8) - binary.BigEndian.PutUint64(aData, blockNo) - aData = append(aData, fileID...) + aData := concatAD(blockNo, fileID) // Get a cipherBS-sized block of memory, copy the nonce into it and truncate to // nonce length cBlock := be.cBlockPool.Get() |