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