<HTML ><HEAD ><TITLE >mcrypt_create_iv</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="PHP Manual" HREF="index.html"><LINK REL="UP" TITLE="Mcrypt Encryption Functions" HREF="ref.mcrypt.html"><LINK REL="PREVIOUS" TITLE="mcrypt_cfb" HREF="function.mcrypt-cfb.html"><LINK REL="NEXT" TITLE="mcrypt_decrypt" HREF="function.mcrypt-decrypt.html"><META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=ISO-8859-1"></HEAD ><BODY CLASS="refentry" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="function.mcrypt-cfb.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="function.mcrypt-decrypt.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="function.mcrypt-create-iv" ></A >mcrypt_create_iv</H1 ><DIV CLASS="refnamediv" ><A NAME="AEN48812" ></A ><P > (PHP 3>= 3.0.8, PHP 4 )</P >mcrypt_create_iv -- Create an initialization vector (IV) from a random source </DIV ><DIV CLASS="refsect1" ><A NAME="AEN48815" ></A ><H2 >Description</H2 >string <B CLASS="methodname" >mcrypt_create_iv</B > ( int size, int source)<BR ></BR ><P > <B CLASS="function" >mcrypt_create_iv()</B > is used to create an IV. </P ><P > <B CLASS="function" >mcrypt_create_iv()</B > takes two arguments, <TT CLASS="parameter" ><I >size</I ></TT > determines the size of the IV, <TT CLASS="parameter" ><I >source</I ></TT > specifies the source of the IV. </P ><P > The source can be MCRYPT_RAND (system random number generator), MCRYPT_DEV_RANDOM (read data from /dev/random) and MCRYPT_DEV_URANDOM (read data from /dev/urandom). If you use MCRYPT_RAND, make sure to call srand() before to initialize the random number generator. </P ><P > <TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" CLASS="EXAMPLE" ><TR ><TD ><DIV CLASS="example" ><A NAME="AEN48834" ></A ><P ><B >Example 1. <B CLASS="function" >mcrypt_create_iv()</B > example</B ></P ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><PRE CLASS="php" ><?php $size = mcrypt_get_iv_size (MCRYPT_CAST_256, MCRYPT_MODE_CFB); $iv = mcrypt_create_iv ($size, MCRYPT_DEV_RANDOM); ?></PRE ></TD ></TR ></TABLE ></DIV ></TD ></TR ></TABLE > </P ><P > The IV is only meant to give an alternative seed to the encryption routines. This IV does not need to be secret at all, though it can be desirable. You even can send it along with your ciphertext without loosing security. </P ><P > More information can be found at <A HREF="http://www.ciphersbyritter.com/GLOSSARY.HTM#IV" TARGET="_top" >http://www.ciphersbyritter.com/GLOSSARY.HTM#IV</A >, <A HREF="http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm" TARGET="_top" >http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm</A > and in chapter 9.3 of Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of this topic. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="function.mcrypt-cfb.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="function.mcrypt-decrypt.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >mcrypt_cfb</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ref.mcrypt.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >mcrypt_decrypt</TD ></TR ></TABLE ></DIV ></BODY ></HTML >