aespipe - AES encrypting or decrypting pipe
aespipe [options] <inputfile >outputfile
aespipe reads from standard input and writes to standard output. It can
be used to create and restore encrypted tar or cpio archives. It can be used
to encrypt and decrypt loop-AES compatible encrypted disk images.
aespipe encrypts and decrypts blocks of data. If you are looking for
general purpose encrypting tool that preserves data size at byte granularity,
then please take a look at GnuPG.
The AES cipher is used in CBC (cipher block chaining) mode. Data is encrypted
and decrypted in 512 byte chains.
aespipe supports three key setup
modes; single-key, multi-key-v2 and multi-key-v3 modes. Single-key mode uses
simple sector IV and one AES key to encrypt and decrypt all data sectors.
Multi-key-v2 mode uses cryptographically more secure MD5 IV and 64 different
AES keys to encrypt and decrypt data sectors. In multi-key mode first key is
used for first sector, second key for second sector, and so on. Multi-key-v3
is same as multi-key-v2 except is uses one extra 65th key as additional input
to MD5 IV computation. See -K option for more information about how to enable
multi-key-v3 mode.
Recommended key setup mode is multi-key-v3, which is based on gpg encrypted key
files. In this mode, the passphrase is protected against optimized dictionary
attacks via salting and key iteration of gpg. Passphrase length should be 20
characters or more.
Single-key mode preserves input size at 16 byte granularity. Multi-key mode
preserves input size at 512 byte granularity. If input size is not multiple of
16 or 512 bytes, input data is padded with null bytes so that both input and
output sizes are multiples of 16 or 512 bytes.
If "ulimit -l" is set to "unlimited" then
aespipe
attempts to lock its RAM so that encryption keys do not leak to unencrypted
swap. If "ulimit -l" is something other than "unlimited"
then
aespipe will proceed without locked RAM.
-
-A gpgAgentSocket
- Read passphrase of gpg encrypted key file from gpg-agent
instead of the terminal. aespipe runs gpg to decrypt a key file, and gpg
talks to gpg-agent using gpgAgentSocket. Usually this data is in
GPG_AGENT_INFO environment variable. The environment that is passed to gpg
is very minimal. Normally gpg passes some environment variables to
gpg-agent, but in this case, there aren't any. For best results, you may
want to configure gpg-agent so that it "keeps" and uses its own
environment. Defining "keep-tty", "keep-display" and
"pinentry-program" in $HOME/.gnupg/gpg-agent.conf configuration
file is a good start.
-
-C itercountk
- Runs hashed passphrase through itercountk thousand
iterations of AES-256 before using it for data encryption. This consumes
lots of CPU cycles at program start time but not thereafter. In
combination with passphrase seed this slows down dictionary attacks.
Iteration is not done in multi-key mode.
- -d
- Decrypt data. If this option is not specified, default
operation is to encrypt data.
-
-e encryption
- Following encryption types are recognized: AES128
(default), AES192 and AES256. Encryption type names are case insensitive.
AES128 defaults to using SHA-256 passphrase hash, AES192 defaults to using
SHA-384 passphrase hash, and AES256 defaults to using SHA-512 passphrase
hash.
-
-G gpghome
- Set gpg home directory to gpghome, so that gpg uses
public/private keys on gpghome directory. This is only used when
gpgkey file needs to be decrypted using public/private keys. If gpgkey
file is encrypted with symmetric cipher only, public/private keys are not
required and this option has no effect.
-
-H phash
- Uses phash function to hash passphrase. Available
hash functions are sha256, sha384, sha512 and rmd160. unhashed1 and
unhashed2 functions also exist for compatibility with some obsolete
implementations. Hash type names are case insensitive.
-
-K gpgkey
- Passphrase is piped to gpg so that gpg can decrypt file
gpgkey which contains the real keys that are used to encrypt data.
If decryption requires public/private keys and gpghome is not specified,
all users use their own gpg public/private keys to decrypt gpgkey.
Decrypted gpgkey should contain 1 or 64 or 65 keys, each key at
least 20 characters and separated by newline. If decrypted gpgkey
contains 64 or 65 keys, then aespipe is put to multi-key mode. 65th key,
if present, is used as additional input to MD5 IV computation.
-
-O sectornumber
- Set IV offset in 512 byte units. Default is zero. Data is
encrypted in 512 byte CBC chains and each 512 byte chain starts with IV
whose computation depends on offset within the data. This option can be
used to start encryption or decryption in middle of some existing
encrypted disk image.
-
-p fdnumber
- Read the passphrase from file descriptor fdnumber
instead of the terminal. If -K option is not being used (no gpg key file),
then aespipe attempts to read 65 keys from passwdfd, each key at
least 20 characters and separated by newline. If aespipe successfully
reads 64 or 65 keys, then aespipe is put to multi-key mode. If aespipe
encounters end-of-file before 64 keys are read, then only first key is
used in single-key mode.
-
-P cleartextkey
- Read the passphrase from file cleartextkey instead
of the terminal. If -K option is not being used (no gpg key file), then
aespipe attempts to read 65 keys from cleartextkey, each key at
least 20 characters and separated by newline. If aespipe successfully
reads 64 or 65 keys, then aespipe is put to multi-key mode. If aespipe
encounters end-of-file before 64 keys are read, then only first key is
used in single-key mode. If both -p and -P options are used, then -p
option takes precedence. These are equivalent:
aespipe -p3 -K foo.gpg -e AES128 ... 3<someFileName
aespipe -P someFileName -K foo.gpg -e AES128 ...
In first line of above example, in addition to normal open file descriptors
(0==stdin 1==stdout 2==stderr), shell opens the file and passes open file
descriptor to started aespipe program. In second line of above example,
aespipe opens the file itself.
- -q
- Be quiet and don't complain about write errors.
-
-S pseed
- Sets encryption passphrase seed pseed which is
appended to user supplied passphrase before hashing. Using different seeds
makes dictionary attacks slower but does not prevent them if user supplied
passphrase is guessable. Seed is not used in multi-key mode.
- -T
- Asks passphrase twice instead of just once.
- -v
- Verbose mode. Prints diagnostics to stderr about key
length, single/multi key mode, and selected code optimizations
(x86/amd64/padlock/intelaes).
-
-w number
- Wait number seconds before asking passphrase.
aespipe returns 0 on success, nonzero on failure.
Source is available from
http://loop-aes.sourceforge.net/
Jari Ruusu