package pathiv import ( "crypto/sha256" "encoding/binary" "github.com/rfjakob/gocryptfs/internal/nametransform" ) // Purpose identifies for which purpose the IV will be used. This is mixed into the // derivation. type Purpose string const ( // PurposeDirIV means the value will be used as a directory IV PurposeDirIV Purpose = "DIRIV" // PurposeFileID means the value will be used as the file ID in the file header PurposeFileID Purpose = "FILEID" // PurposeSymlinkIV means the value will be used as the IV for symlink encryption PurposeSymlinkIV Purpose = "SYMLINKIV" // PurposeBlock0IV means the value will be used as the IV of ciphertext block #0. PurposeBlock0IV Purpose = "BLOCK0IV" ) // Derive derives an IV from an encrypted path by hashing it with sha256 func Derive(path string, purpose Purpose) []byte { // Use null byte as separator as it cannot occur in the path extended := []byte(path + "\000" + string(purpose)) hash := sha256.Sum256(extended) return hash[:nametransform.DirIVLen] } // FileIVs contains both IVs that are needed to create a file. type FileIVs struct { ID []byte Block0IV []byte } // DeriveFile derives both IVs that are needed to create a file and returns them // in a container struct. func DeriveFile(path string) (fileIVs FileIVs) { fileIVs.ID = Derive(path, PurposeFileID) fileIVs.Block0IV = Derive(path, PurposeBlock0IV) return fileIVs } // BlockIV returns the block IV for block number "blockNo". "block0iv" is the block // IV of block #0. func BlockIV(block0iv []byte, blockNo uint64) []byte { iv := make([]byte, len(block0iv)) copy(iv, block0iv) // Add blockNo to one half of the iv lowBytes := iv[8:] lowInt := binary.BigEndian.Uint64(lowBytes) binary.BigEndian.PutUint64(lowBytes, lowInt+blockNo) return iv }