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|
package cryptfs
// CryptFS is the crypto backend of GoCryptFS
import (
"crypto/aes"
"crypto/cipher"
"fmt"
)
const (
DEFAULT_PLAINBS = 4096
KEY_LEN = 32 // AES-256
AUTH_TAG_LEN = 16
DIRIV_LEN = 16 // identical to AES block size
DIRIV_FILENAME = "gocryptfs.diriv"
)
type CryptFS struct {
blockCipher cipher.Block
gcm cipher.AEAD
gcmIVLen int
gcmIVGen nonceGenerator
plainBS uint64
cipherBS uint64
// Stores an all-zero block of size cipherBS
allZeroBlock []byte
// DirIV cache for filename encryption
DirIVCacheEnc DirIVCache
}
func NewCryptFS(key []byte, useOpenssl bool, plaintextNames bool, GCMIV128 bool) *CryptFS {
if len(key) != KEY_LEN {
panic(fmt.Sprintf("Unsupported key length %d", len(key)))
}
b, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
// We want the IV size in bytes
gcmIV := 96 / 8
if GCMIV128 {
gcmIV = 128 / 8
}
var gcm cipher.AEAD
if useOpenssl {
gcm = opensslGCM{key}
} else {
gcm, err = cipher.NewGCMWithNonceSize(b, gcmIV)
if err != nil {
panic(err)
}
}
plainBS := DEFAULT_PLAINBS
cipherBS := plainBS + gcmIV + AUTH_TAG_LEN
return &CryptFS{
blockCipher: b,
gcm: gcm,
gcmIVLen: gcmIV,
gcmIVGen: nonceGenerator{nonceLen: gcmIV},
plainBS: uint64(plainBS),
cipherBS: uint64(cipherBS),
allZeroBlock: make([]byte, cipherBS),
}
}
// Get plaintext block size
func (be *CryptFS) PlainBS() uint64 {
return be.plainBS
}
// Per-block storage overhead
func (be *CryptFS) BlockOverhead() uint64 {
return be.cipherBS - be.plainBS
}
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