MAN page from OpenSuSE aespipe-2.4e-2.2.x86_64.rpm

AESPIPE

Section: COMMANDS (1)
Updated: February 23 2011
Index

NAME

aespipe - AES encrypting or decrypting pipe

SYNOPSIS

aespipe[options] <inputfile >outputfile

DESCRIPTION

aespipereads from standard input and writes to standard output. It can be used tocreate and restore encrypted tar or cpio archives. It can be used to encryptand decrypt loop-AES compatible encrypted disk images.aespipeencrypts and decrypts blocks of data. If you are looking for general purposeencrypting tool that preserves data size at byte granularity, then pleasetake a look at GnuPG.

The AES cipher is used in CBC (cipher block chaining) mode. Data isencrypted and decrypted in 512 byte chains.aespipesupports three key setup modes; single-key, multi-key-v2 and multi-key-v3modes. Single-key mode uses simple sector IV and one AES key to encrypt anddecrypt all data sectors. Multi-key-v2 mode uses cryptographically moresecure 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 secondsector, and so on. Multi-key-v3 is same as multi-key-v2 except is uses oneextra 65th key as additional input to MD5 IV computation. See -K option formore information about how to enable multi-key-v3 mode.

Recommended key setup mode is multi-key-v3, which is based on gpg encryptedkey files. In this mode, the passphrase is protected against optimizeddictionary attacks via salting and key iteration of gpg. Passphrase lengthshould be 20 characters or more.

Single-key mode preserves input size at 16 byte granularity. Multi-key modepreserves input size at 512 byte granularity. If input size is not multipleof 16 or 512 bytes, input data is padded with null bytes so that both inputand output sizes are multiples of 16 or 512 bytes.

If "ulimit -l" is set to "unlimited" thenaespipeattempts to lock its RAM so that encryption keys do not leak to unencryptedswap. If "ulimit -l" is something other than "unlimited" thenaespipewill proceed without locked RAM.

OPTIONS

-A gpgAgentSocket

Read passphrase of gpg encrypted key file from gpg-agent instead of theterminal. aespipe runs gpg to decrypt a key file, and gpg talks to gpg-agentusing gpgAgentSocket. Usually this data is in GPG_AGENT_INFOenvironment variable. The environment that is passed to gpg is very minimal.Normally gpg passes some environment variables to gpg-agent, but in thiscase, there aren't any. For best results, you may want to configuregpg-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-256before using it for data encryption. This consumes lots of CPU cycles atprogram start time but not thereafter. In combination with passphrase seedthis slows down dictionary attacks. Iteration is not done in multi-key mode.

-d

Decrypt data. If this option is not specified, default operation is toencrypt data.

-e encryption

Following encryption types are recognized: AES128 (default), AES192and AES256. Encryption type names are case insensitive. AES128 defaults tousing 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/privatekeys on gpghome directory. This is only used when gpgkey file needs tobe decrypted using public/private keys. If gpgkey file is encrypted withsymmetric cipher only, public/private keys are not required and this optionhas no effect.

-H phash

Uses phash function to hash passphrase. Available hash functions aresha256, sha384, sha512 and rmd160. unhashed1 and unhashed2 functions alsoexist for compatibility with some obsolete implementations. Hash type namesare case insensitive.

-K gpgkey

Passphrase is piped to gpg so that gpg can decrypt file gpgkey whichcontains the real keys that are used to encrypt data. If decryption requirespublic/private keys and gpghome is not specified, all users use their owngpg public/private keys to decrypt gpgkey. Decrypted gpgkeyshould contain 1 or 64 or 65 keys, each key at least 20 characters andseparated by newline. If decrypted gpgkey contains 64 or 65 keys, thenaespipe is put to multi-key mode. 65th key, if present, is used asadditional input to MD5 IV computation.

-O sectornumber

Set IV offset in 512 byte units. Default is zero. Data is encrypted in 512byte CBC chains and each 512 byte chain starts with IV whose computationdepends on offset within the data. This option can be used to startencryption or decryption in middle of some existing encrypted disk image.

-p fdnumber

Read the passphrase from file descriptor fdnumber instead of theterminal. If -K option is not being used (no gpg key file), then aespipeattempts to read 65 keys from passwdfd, each key at least 20characters and separated by newline. If aespipe successfully reads 64 or 65keys, then aespipe is put to multi-key mode. If aespipe encountersend-of-file before 64 keys are read, then only first key is used insingle-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 read65 keys from cleartextkey, each key at least 20 characters andseparated by newline. If aespipe successfully reads 64 or 65 keys, thenaespipe is put to multi-key mode. If aespipe encounters end-of-file before64 keys are read, then only first key is used in single-key mode. If both -pand -P options are used, then -p option takes precedence. These areequivalent:

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 filedescriptor 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 suppliedpassphrase before hashing. Using different seeds makes dictionary attacksslower 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/multikey mode, and selected code optimizations (x86/amd64/padlock/intelaes).

-w number

Wait number seconds before asking passphrase.

RETURN VALUE

aespipereturns 0 on success, nonzero on failure.

AVAILABILITY

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

AUTHORS

Jari Ruusu

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