aespipe - AES encrypting or decrypting pipe

Authors

       Jari Ruusu

LINUX                                           February 23 2011                                      AESPIPE(1)

Availability

       Source is available from http://loop-aes.sourceforge.net/

Description

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.

Name

       aespipe - AES encrypting or decrypting pipe

Options

-AgpgAgentSocket
              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.

       -Citercountk
              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.

       -eencryption
              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.

       -Ggpghome
              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.

       -Hphash
              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.

       -Kgpgkey
              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.

       -Osectornumber
              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.

       -pfdnumber
              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.

       -Pcleartextkey
              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.

       -Spseed
              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).

       -wnumber
              Wait number seconds before asking passphrase.

Return Value

aespipe returns 0 on success, nonzero on failure.

Synopsis

aespipe [options] <inputfile >outputfile