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<HEAD><TITLE> The ice and deice applications </TITLE></HEAD>
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<H1>The ice and deice applications </H1>
<H3>Synopsis</H3>
<DL>
<DD> <CODE>ice [ -CDNZ ] [ -p passwd ] [ -l level ] [ file ... ]</CODE>
<BR><BR>
<DD> <CODE>deice [ -CNZ ] [ -p passwd ] [ -l level ] [ file ... ]</CODE>
</DL>
<H3>Description</H3>
<P>
<B>ice</B> and <B>deice</B> are programs for encrypting and decrypting
files using the ICE (Information Concealment Engine) encryption algorithm.
The data is encrypted in Cipher Block Chaining (CBC) mode, with an
initialization vector by default obtained from the <B>gettimeofday</B>(2)
function. </P>
<P>
The ICE encryption algorithm allows key lengths of any multiple of 64 bits
by specifying the encryption <EM>level</EM>. Specifying a level greater
than 1 allows long passwords, and correspondingly higher security.
The drawback is slower encryption. </P>
<P>
This program only uses the lower 7 bits from each character in the
password, so the first 10 characters are significant when using
levels 0 or 1. For higher levels <EM>n</EM>, the key size is 64<EM>n</EM>,
so the useful password length will be (64<EM>n</EM> + 6)/7. Short passwords
will be padded out with zeroes. </P>
<P>
The <B>deice</B> program is typically a symbolic link to the ice
executable, since the program automatically uses decrypt mode if the
name of the executable begins with the characters "de". </P>
<P>
When encrypting, a new file will be created with a <EM>.ice</EM>
suffix, and the original file deleted. Before deletion, the original
file is overwritten with zeroes to minimize the chance that the
data remains in the filesystem. Where possible the new file will
have the same permissions as the original. If no files are specified,
data will be read from standard input. </P>
<P>
For decryption, the files must have a <EM>.ice</EM> suffix, or
there must be a <EM>file.ice</EM> for every file. The program will
check that the data is ICE-encrypted, but it will give no indication
as to whether the correct password is being used, so beware. </P>
<P>
The encrypted file format contains "ice" as the first three characters,
followed the value of the character "0" added to the ICE level being used.
The next eight bytes contain the initialization vector, followed by the
actual encrypted data. This information, plus padding of the last block,
will increase the file size by between 13 and 20 bytes. </P>
<H3>Options</H3>
<DL>
<DT> <B>-C</B>
<DD> Send encrypted/decrypted output to standard output.
<BR><BR>
<DT> <B>-D</B>
<DD> Decrypt the data. This is the default in <B>deice</B>.
<BR><BR>
<DT> <B>-N</B>
<DD> Do not ask for confirmation of the password when an interactive
password is required. By default, the user has to type the password
twice.
<BR><BR>
<DT> <B>-Z</B>
<DD> Use a zero initializing vector. Only useful if identical files have
to encrypt identically. The initializing vector is otherwise set from
time of day information. In the case of decryption the vector is read
from the data anyway, so this flag is ignored.
<BR><BR>
<DT> <B>-p</B> <EM>password</EM>
<DD> The password used to encrypt/decrypt the data. If this is set, no
interactive password is required. This password is zeroed out at the
first opportunity to prevent it appearing in the process table.
<BR><BR>
<DT> <B>-l</B> <EM>level</EM>
<DD> The ICE level used to encrypt the data. Defaults to 1. This is
ignored during decryption, since the level information is stored in
the data.
</DL>
<H3>Examples</H3>
<P>
The following command will encrypt the file <EM>foo</EM>, and store
the result in <EM>foo.ice</EM>. The user will be prompted twice for
a password, which will have the first 10 of its characters used. </P>
<DL>
<DD> <CODE> ice foo </CODE>
</DL>
<P>
The next example will encrypt the same file with a command-line
password using level 2 ICE. </P>
<DL>
<DD> <CODE> ice -l2 -p"The first 19 charac" foo </CODE>
</DL>
<P>
The resulting file can be decrypted with </P>
<DL>
<DD> <CODE> deice -p"The first 19 charac" foo.ice </CODE>
</DL>
<H3>Author</H3>
<P>
This application was written by Matthew Kwan, who can be reached
at <A HREF="mailto:mkwan@darkside.com.au">mkwan@darkside.com.au</A> </P>
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