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authorJakob Unterwurzacher2015-11-01 12:11:36 +0100
committerJakob Unterwurzacher2015-11-01 12:11:36 +0100
commit902babdf22199d73171716e643f1ffbb65e6fb48 (patch)
treec3194bce9fd9b4db0a569fca3b5041abd278be70 /cryptfs/address_translation.go
parent14276c96328a1a1ad2b354c65d8db7fa720559e1 (diff)
Refactor ciphertext <-> plaintext offset translation functions
Move all the intelligence into the new file address_translation.go. That the calculations were spread out too much became apparent when adding the file header. This should make the code much easier to modify in the future.
Diffstat (limited to 'cryptfs/address_translation.go')
-rw-r--r--cryptfs/address_translation.go79
1 files changed, 79 insertions, 0 deletions
diff --git a/cryptfs/address_translation.go b/cryptfs/address_translation.go
new file mode 100644
index 0000000..dfc6ef9
--- /dev/null
+++ b/cryptfs/address_translation.go
@@ -0,0 +1,79 @@
+package cryptfs
+
+// CryptFS methods that translate offsets between ciphertext and plaintext
+
+// get the block number at plain-text offset
+func (be *CryptFS) PlainOffToBlockNo(plainOffset uint64) uint64 {
+ return plainOffset / be.plainBS
+}
+
+// get the block number at ciphter-text offset
+func (be *CryptFS) CipherOffToBlockNo(cipherOffset uint64) uint64 {
+ return (cipherOffset - HEADER_LEN) / be.cipherBS
+}
+
+// get ciphertext offset of block "blockNo"
+func (be *CryptFS) BlockNoToCipherOff(blockNo uint64) uint64 {
+ return HEADER_LEN + blockNo*be.cipherBS
+}
+
+// get plaintext offset of block "blockNo"
+func (be *CryptFS) BlockNoToPlainOff(blockNo uint64) uint64 {
+ return blockNo * be.plainBS
+}
+
+// PlainSize - calculate plaintext size from ciphertext size
+func (be *CryptFS) CipherSizeToPlainSize(cipherSize uint64) uint64 {
+
+ // Zero sized files stay zero-sized
+ if cipherSize == 0 {
+ return 0
+ }
+
+ // Block number at last byte
+ blockNo := be.CipherOffToBlockNo(cipherSize - 1)
+ blockCount := blockNo + 1
+
+ overhead := BLOCK_OVERHEAD*blockCount + HEADER_LEN
+
+ return cipherSize - overhead
+}
+
+// CipherSize - calculate ciphertext size from plaintext size
+func (be *CryptFS) PlainSizeToCipherSize(plainSize uint64) uint64 {
+
+ // Block number at last byte
+ blockNo := be.PlainOffToBlockNo(plainSize - 1)
+ blockCount := blockNo + 1
+
+ overhead := BLOCK_OVERHEAD*blockCount + HEADER_LEN
+
+ return plainSize + overhead
+}
+
+// Split a plaintext byte range into (possibly partial) blocks
+func (be *CryptFS) ExplodePlainRange(offset uint64, length uint64) []intraBlock {
+ var blocks []intraBlock
+ var nextBlock intraBlock
+ nextBlock.fs = be
+
+ for length > 0 {
+ nextBlock.BlockNo = be.PlainOffToBlockNo(offset)
+ nextBlock.Skip = offset - be.BlockNoToPlainOff(nextBlock.BlockNo)
+
+ // Minimum of remaining data and remaining space in the block
+ nextBlock.Length = MinUint64(length, be.plainBS-nextBlock.Skip)
+
+ blocks = append(blocks, nextBlock)
+ offset += nextBlock.Length
+ length -= nextBlock.Length
+ }
+ return blocks
+}
+
+func MinUint64(x uint64, y uint64) uint64 {
+ if x < y {
+ return x
+ }
+ return y
+}