package contentenc import ( "github.com/rfjakob/gocryptfs/internal/toggledlog" ) // Contentenc methods that translate offsets between ciphertext and plaintext // get the block number at plain-text offset func (be *ContentEnc) PlainOffToBlockNo(plainOffset uint64) uint64 { return plainOffset / be.plainBS } // get the block number at ciphter-text offset func (be *ContentEnc) CipherOffToBlockNo(cipherOffset uint64) uint64 { return (cipherOffset - HEADER_LEN) / be.cipherBS } // get ciphertext offset of block "blockNo" func (be *ContentEnc) BlockNoToCipherOff(blockNo uint64) uint64 { return HEADER_LEN + blockNo*be.cipherBS } // get plaintext offset of block "blockNo" func (be *ContentEnc) BlockNoToPlainOff(blockNo uint64) uint64 { return blockNo * be.plainBS } // PlainSize - calculate plaintext size from ciphertext size func (be *ContentEnc) CipherSizeToPlainSize(cipherSize uint64) uint64 { // Zero sized files stay zero-sized if cipherSize == 0 { return 0 } if cipherSize == HEADER_LEN { toggledlog.Warn.Printf("cipherSize %d == header size: interrupted write?\n", cipherSize) return 0 } if cipherSize < HEADER_LEN { toggledlog.Warn.Printf("cipherSize %d < header size %d: corrupt file\n", cipherSize, HEADER_LEN) return 0 } // Block number at last byte blockNo := be.CipherOffToBlockNo(cipherSize - 1) blockCount := blockNo + 1 overhead := be.BlockOverhead()*blockCount + HEADER_LEN return cipherSize - overhead } // CipherSize - calculate ciphertext size from plaintext size func (be *ContentEnc) PlainSizeToCipherSize(plainSize uint64) uint64 { // Block number at last byte blockNo := be.PlainOffToBlockNo(plainSize - 1) blockCount := blockNo + 1 overhead := be.BlockOverhead()*blockCount + HEADER_LEN return plainSize + overhead } // Split a plaintext byte range into (possibly partial) blocks func (be *ContentEnc) 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 (be *ContentEnc) BlockOverhead() uint64 { return be.cipherBS - be.plainBS } func MinUint64(x uint64, y uint64) uint64 { if x < y { return x } return y }