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Diffstat (limited to 'internal/pathiv/pathiv.go')
-rw-r--r--internal/pathiv/pathiv.go13
1 files changed, 13 insertions, 0 deletions
diff --git a/internal/pathiv/pathiv.go b/internal/pathiv/pathiv.go
index aa11b75..08042e9 100644
--- a/internal/pathiv/pathiv.go
+++ b/internal/pathiv/pathiv.go
@@ -2,6 +2,7 @@ package pathiv
import (
"crypto/sha256"
+ "encoding/binary"
"github.com/rfjakob/gocryptfs/internal/nametransform"
)
@@ -42,3 +43,15 @@ func DeriveFile(path string) (fileIVs FileIVs) {
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
+}