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| author |   hongbotian <hongbo.tianhongbo@huawei.com> | 2015-11-30 03:10:21 -0500 |
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| committer | hongbotian <hongbo.tianhongbo@huawei.com> | 2015-11-30 03:10:21 -0500 |
| commit | c0b7206652b2852bc574694e7ba07ba1c2acdc00 (patch) | |
| tree | 5cb95cb0e19e03610525903df46279df2c3b7eb1 /rubbos/app/apache2/manual/ssl/ssl_intro.html.en | |
| parent | b6d3d6e668b793220f2d3af1bc3e828553dc3fe6 (diff) | |
delete app
Change-Id: Id4c572809969ebe89e946e88063eaed262cff3f2
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diff --git a/rubbos/app/apache2/manual/ssl/ssl_intro.html.en b/rubbos/app/apache2/manual/ssl/ssl_intro.html.en deleted file mode 100644 index c3079d4e..00000000 --- a/rubbos/app/apache2/manual/ssl/ssl_intro.html.en +++ /dev/null @@ -1,641 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - This file is generated from xml source: DO NOT EDIT - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - --> -<title>SSL/TLS Strong Encryption: An Introduction - Apache HTTP Server</title> -<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> -<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> -<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /> -<link href="../images/favicon.ico" rel="shortcut icon" /></head> -<body id="manual-page"><div id="page-header"> -<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> -<p class="apache">Apache HTTP Server Version 2.0</p> -<img alt="" src="../images/feather.gif" /></div> -<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> -<div id="path"> -<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">SSL/TLS</a></div><div id="page-content"><div id="preamble"><h1>SSL/TLS Strong Encryption: An Introduction</h1> -<div class="toplang"> -<p><span>Available Languages: </span><a href="../en/ssl/ssl_intro.html" title="English"> en </a> | -<a href="../ja/ssl/ssl_intro.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p> -</div> - -<blockquote> -<p>The nice thing about standards is that there are so many to choose -from. And if you really don't like all the standards you just have to -wait another year until the one arises you are looking for.</p> - -<p class="cite">-- <cite>A. Tanenbaum</cite>, "Introduction to -Computer Networks"</p> -</blockquote> - -<p>As an introduction this chapter is aimed at readers who are familiar -with the Web, HTTP, and Apache, but are not security experts. It is not -intended to be a definitive guide to the SSL protocol, nor does it discuss -specific techniques for managing certificates in an organization, or the -important legal issues of patents and import and export restrictions. -Rather, it is intended to provide a common background to mod_ssl users by -pulling together various concepts, definitions, and examples as a starting -point for further exploration.</p> - -<p>The presented content is mainly derived, with permission by the author, -from the article <a href="http://home.earthlink.net/~fjhirsch/Papers/wwwj/article.html">Introducing -SSL and Certificates using SSLeay</a> from <a href="http://home.earthlink.net/~fjhirsch/">Frederick J. Hirsch</a>, of The -Open Group Research Institute, which was published in <a href="http://www.ora.com/catalog/wjsum97/">Web Security: A Matter of -Trust</a>, World Wide Web Journal, Volume 2, Issue 3, Summer 1997. -Please send any positive feedback to <a href="mailto:hirsch@fjhirsch.com">Frederick Hirsch</a> (the original -article author) and all negative feedback to <a href="mailto:rse@engelschall.com">Ralf S. Engelschall</a> (the -<code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> author).</p> -</div> -<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#cryptographictech">Cryptographic Techniques</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#certificates">Certificates</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#ssl">Secure Sockets Layer (SSL)</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#references">References</a></li> -</ul></div> -<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="cryptographictech" id="cryptographictech">Cryptographic Techniques</a></h2> - -<p>Understanding SSL requires an understanding of cryptographic -algorithms, message digest functions (aka. one-way or hash functions), and -digital signatures. These techniques are the subject of entire books (see -for instance [<a href="#AC96">AC96</a>]) and provide the basis for privacy, -integrity, and authentication.</p> - -<h3><a name="cryptographicalgo" id="cryptographicalgo">Cryptographic Algorithms</a></h3> - - <p>Suppose Alice wants to send a message to her bank to transfer some - money. Alice would like the message to be private, since it will - include information such as her account number and transfer amount. One - solution is to use a cryptographic algorithm, a technique that would - transform her message into an encrypted form, unreadable except by - those it is intended for. Once in this form, the message may only be - interpreted through the use of a secret key. Without the key the - message is useless: good cryptographic algorithms make it so difficult - for intruders to decode the original text that it isn't worth their - effort.</p> - - <p>There are two categories of cryptographic algorithms: conventional - and public key.</p> - - <dl> - <dt>Conventional cryptography</dt> - <dd>also known as symmetric cryptography, requires the sender and - receiver to share a key: a secret piece of information that may be - used to encrypt or decrypt a message. If this key is secret, then - nobody other than the sender or receiver may read the message. If - Alice and the bank know a secret key, then they may send each other - private messages. The task of privately choosing a key before - communicating, however, can be problematic.</dd> - - <dt>Public key cryptography</dt> - <dd>also known as asymmetric cryptography, solves the key exchange - problem by defining an algorithm which uses two keys, each of which - may be used to encrypt a message. If one key is used to encrypt a - message then the other must be used to decrypt it. This makes it - possible to receive secure messages by simply publishing one key - (the public key) and keeping the other secret (the private key).</dd> - </dl> - - <p>Anyone may encrypt a message using the public key, but only the - owner of the private key will be able to read it. In this way, Alice - may send private messages to the owner of a key-pair (the bank), by - encrypting it using their public key. Only the bank will be able to - decrypt it.</p> - - -<h3><a name="messagedigests" id="messagedigests">Message Digests</a></h3> - - <p>Although Alice may encrypt her message to make it private, there - is still a concern that someone might modify her original message or - substitute it with a different one, in order to transfer the money - to themselves, for instance. One way of guaranteeing the integrity - of Alice's message is to create a concise summary of her message and - send this to the bank as well. Upon receipt of the message, the bank - creates its own summary and compares it with the one Alice sent. If - they agree then the message was received intact.</p> - - <p>A summary such as this is called a <dfn>message digest</dfn>, <em>one-way -function</em> or <em>hash function</em>. Message digests are used to create -short, fixed-length representations of longer, variable-length messages. -Digest algorithms are designed to produce unique digests for different -messages. Message digests are designed to make it too difficult to determine -the message from the digest, and also impossible to find two different -messages which create the same digest -- thus eliminating the possibility of -substituting one message for another while maintaining the same digest.</p> -<p>Another challenge that Alice faces is finding a way to send the digest to the -bank securely; when this is achieved, the integrity of the associated message -is assured. One way to do this is to include the digest in a digital -signature.</p> - - -<h3><a name="digitalsignatures" id="digitalsignatures">Digital Signatures</a></h3> -<p>When Alice sends a message to the bank, the bank needs to ensure that the -message is really from her, so an intruder does not request a transaction -involving her account. A <em>digital signature</em>, created by Alice and -included with the message, serves this purpose.</p> - -<p>Digital signatures are created by encrypting a digest of the message, -and other information (such as a sequence number) with the sender's -private key. Though anyone may <em>decrypt</em> the signature using the public -key, only the signer knows the private key. This means that only they may -have signed it. Including the digest in the signature means the signature is -only good for that message; it also ensures the integrity of the message since -no one can change the digest and still sign it.</p> -<p>To guard against interception and reuse of the signature by an intruder at a -later date, the signature contains a unique sequence number. This protects -the bank from a fraudulent claim from Alice that she did not send the message --- only she could have signed it (non-repudiation).</p> - -</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="certificates" id="certificates">Certificates</a></h2> - -<p>Although Alice could have sent a private message to the bank, signed -it, and ensured the integrity of the message, she still needs to be sure -that she is really communicating with the bank. This means that she needs -to be sure that the public key she is using corresponds to the bank's -private key. Similarly, the bank also needs to verify that the message -signature really corresponds to Alice's signature.</p> - -<p>If each party has a certificate which validates the other's identity, -confirms the public key, and is signed by a trusted agency, then they both -will be assured that they are communicating with whom they think they are. -Such a trusted agency is called a <em>Certificate Authority</em>, and -certificates are used for authentication.</p> - -<h3><a name="certificatecontents" id="certificatecontents">Certificate Contents</a></h3> - - <p>A certificate associates a public key with the real identity of - an individual, server, or other entity, known as the subject. As - shown in <a href="#table1">Table 1</a>, information about the subject - includes identifying information (the distinguished name), and the - public key. It also includes the identification and signature of the - Certificate Authority that issued the certificate, and the period of - time during which the certificate is valid. It may have additional - information (or extensions) as well as administrative information - for the Certificate Authority's use, such as a serial number.</p> - - <h4><a name="table1" id="table1">Table 1: Certificate Information</a></h4> - - <table> - - <tr><th>Subject</th> - <td>Distinguished Name, Public Key</td></tr> - <tr><th>Issuer</th> - <td>Distinguished Name, Signature</td></tr> - <tr><th>Period of Validity</th> - <td>Not Before Date, Not After Date</td></tr> - <tr><th>Administrative Information</th> - <td>Version, Serial Number</td></tr> - <tr><th>Extended Information</th> - <td>Basic Constraints, Netscape Flags, etc.</td></tr> - </table> - - - <p>A distinguished name is used to provide an identity in a specific - context -- for instance, an individual might have a personal - certificate as well as one for their identity as an employee. - Distinguished names are defined by the X.509 standard [<a href="#X509">X509</a>], which defines the fields, field names, and - abbreviations used to refer to the fields (see <a href="#table2">Table - 2</a>).</p> - - <h4><a name="table2" id="table2">Table 2: Distinguished Name Information</a></h4> - - <table class="bordered"> - - <tr><th>DN Field</th> - <th>Abbrev.</th> - <th>Description</th> - <th>Example</th></tr> - <tr><td>Common Name</td> - <td>CN</td> - <td>Name being certified</td> - <td>CN=Joe Average</td></tr> - <tr><td>Organization or Company</td> - <td>O</td> - <td>Name is associated with this<br />organization</td> - <td>O=Snake Oil, Ltd.</td></tr> - <tr><td>Organizational Unit</td> - <td>OU</td> - <td>Name is associated with this <br />organization unit, such - as a department</td> - <td>OU=Research Institute</td></tr> - <tr><td>City/Locality</td> - <td>L</td> - <td>Name is located in this City</td> - <td>L=Snake City</td></tr> - <tr><td>State/Province</td> - <td>ST</td> - <td>Name is located in this State/Province</td> - <td>ST=Desert</td></tr> - <tr><td>Country</td> - <td>C</td> - <td>Name is located in this Country (ISO code)</td> - <td>C=XZ</td></tr> - </table> - - - <p>A Certificate Authority may define a policy specifying which - distinguished field names are optional, and which are required. It - may also place requirements upon the field contents, as may users of - certificates. As an example, a Netscape browser requires that the - Common Name for a certificate representing a server has a name which - matches a wildcard pattern for the domain name of that server, such - as <code>*.snakeoil.com</code>.</p> - - <p>The binary format of a certificate is defined using the ASN.1 - notation [<a href="#X208">X208</a>] [<a href="#PKCS">PKCS</a>]. This - notation defines how to specify the contents, and encoding rules - define how this information is translated into binary form. The binary - encoding of the certificate is defined using Distinguished Encoding - Rules (DER), which are based on the more general Basic Encoding Rules - (BER). For those transmissions which cannot handle binary, the binary - form may be translated into an ASCII form by using Base64 encoding - [<a href="#MIME">MIME</a>]. This encoded version is called PEM encoded - (the name comes from "Privacy Enhanced Mail"), when placed between - begin and end delimiter lines as illustrated in the following - example.</p> - - <div class="example"><h3>Example of a PEM-encoded certificate (snakeoil.crt)</h3><pre>-----BEGIN CERTIFICATE----- -MIIC7jCCAlegAwIBAgIBATANBgkqhkiG9w0BAQQFADCBqTELMAkGA1UEBhMCWFkx -FTATBgNVBAgTDFNuYWtlIERlc2VydDETMBEGA1UEBxMKU25ha2UgVG93bjEXMBUG -A1UEChMOU25ha2UgT2lsLCBMdGQxHjAcBgNVBAsTFUNlcnRpZmljYXRlIEF1dGhv -cml0eTEVMBMGA1UEAxMMU25ha2UgT2lsIENBMR4wHAYJKoZIhvcNAQkBFg9jYUBz -bmFrZW9pbC5kb20wHhcNOTgxMDIxMDg1ODM2WhcNOTkxMDIxMDg1ODM2WjCBpzEL -MAkGA1UEBhMCWFkxFTATBgNVBAgTDFNuYWtlIERlc2VydDETMBEGA1UEBxMKU25h -a2UgVG93bjEXMBUGA1UEChMOU25ha2UgT2lsLCBMdGQxFzAVBgNVBAsTDldlYnNl -cnZlciBUZWFtMRkwFwYDVQQDExB3d3cuc25ha2VvaWwuZG9tMR8wHQYJKoZIhvcN -AQkBFhB3d3dAc25ha2VvaWwuZG9tMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKB -gQDH9Ge/s2zcH+da+rPTx/DPRp3xGjHZ4GG6pCmvADIEtBtKBFAcZ64n+Dy7Np8b -vKR+yy5DGQiijsH1D/j8HlGE+q4TZ8OFk7BNBFazHxFbYI4OKMiCxdKzdif1yfaa -lWoANFlAzlSdbxeGVHoT0K+gT5w3UxwZKv2DLbCTzLZyPwIDAQABoyYwJDAPBgNV -HRMECDAGAQH/AgEAMBEGCWCGSAGG+EIBAQQEAwIAQDANBgkqhkiG9w0BAQQFAAOB -gQAZUIHAL4D09oE6Lv2k56Gp38OBDuILvwLg1v1KL8mQR+KFjghCrtpqaztZqcDt -2q2QoyulCgSzHbEGmi0EsdkPfg6mp0penssIFePYNI+/8u9HT4LuKMJX15hxBam7 -dUHzICxBVC1lnHyYGjDuAMhe396lYAn8bCld1/L4NMGBCQ== ------END CERTIFICATE-----</pre></div> - - -<h3><a name="certificateauthorities" id="certificateauthorities">Certificate Authorities</a></h3> - - <p>By first verifying the information in a certificate request - before granting the certificate, the Certificate Authority assures - the identity of the private key owner of a key-pair. For instance, - if Alice requests a personal certificate, the Certificate Authority - must first make sure that Alice really is the person the certificate - request claims.</p> - - <h4><a name="certificatechains" id="certificatechains">Certificate Chains</a></h4> - - <p>A Certificate Authority may also issue a certificate for - another Certificate Authority. When examining a certificate, - Alice may need to examine the certificate of the issuer, for each - parent Certificate Authority, until reaching one which she has - confidence in. She may decide to trust only certificates with a - limited chain of issuers, to reduce her risk of a "bad" certificate - in the chain.</p> - - - <h4><a name="rootlevelca" id="rootlevelca">Creating a Root-Level CA</a></h4> - - <p>As noted earlier, each certificate requires an issuer to assert - the validity of the identity of the certificate subject, up to - the top-level Certificate Authority (CA). This presents a problem: - Since this is who vouches for the certificate of the top-level - authority, which has no issuer? In this unique case, the - certificate is "self-signed", so the issuer of the certificate is - the same as the subject. As a result, one must exercise extra care - in trusting a self-signed certificate. The wide publication of a - public key by the root authority reduces the risk in trusting this - key -- it would be obvious if someone else publicized a key - claiming to be the authority. Browsers are preconfigured to trust - well-known certificate authorities.</p> - - <p>A number of companies, such as <a href="http://www.thawte.com/">Thawte</a> and <a href="http://www.verisign.com/">VeriSign</a> - have established themselves as Certificate Authorities. These - companies provide the following services:</p> - - <ul> - <li>Verifying certificate requests</li> - <li>Processing certificate requests</li> - <li>Issuing and managing certificates</li> - </ul> - - <p>It is also possible to create your own Certificate Authority. - Although risky in the Internet environment, it may be useful - within an Intranet where the organization can easily verify the - identities of individuals and servers.</p> - - - <h4><a name="certificatemanagement" id="certificatemanagement">Certificate Management</a></h4> - - <p>Establishing a Certificate Authority is a responsibility which - requires a solid administrative, technical, and management - framework. Certificate Authorities not only issue certificates, - they also manage them -- that is, they determine how long - certificates are valid, they renew them, and they keep lists of - certificates that have already been issued but are no longer valid - (Certificate Revocation Lists, or CRLs). Say Alice is entitled to - a certificate as an employee of a company. Say too, that the - certificate needs to be revoked when Alice leaves the company. Since - certificates are objects that get passed around, it is impossible - to tell from the certificate alone that it has been revoked. When - examining certificates for validity, therefore, it is necessary to - contact the issuing Certificate Authority to check CRLs -- this - is not usually an automated part of the process.</p> - - <div class="note"><h3>Note</h3> - <p>If you use a Certificate Authority that is not configured into - browsers by default, it is necessary to load the Certificate - Authority certificate into the browser, enabling the browser to - validate server certificates signed by that Certificate Authority. - Doing so may be dangerous, since once loaded, the browser will - accept all certificates signed by that Certificate Authority.</p> - </div> - - - -</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="ssl" id="ssl">Secure Sockets Layer (SSL)</a></h2> - -<p>The Secure Sockets Layer protocol is a protocol layer which may be -placed between a reliable connection-oriented network layer protocol -(e.g. TCP/IP) and the application protocol layer (e.g. HTTP). SSL provides -for secure communication between client and server by allowing mutual -authentication, the use of digital signatures for integrity, and encryption -for privacy.</p> - -<p>The protocol is designed to support a range of choices for specific -algorithms used for cryptography, digests, and signatures. This allows -algorithm selection for specific servers to be made based on legal, export -or other concerns, and also enables the protocol to take advantage of new -algorithms. Choices are negotiated between client and server at the start -of establishing a protocol session.</p> - -<h3><a name="table4" id="table4">Table 4: Versions of the SSL protocol</a></h3> - - <table class="bordered"> - - <tr><th>Version</th> - <th>Source</th> - <th>Description</th> - <th>Browser Support</th></tr> - <tr><td>SSL v2.0</td> - <td>Vendor Standard (from Netscape Corp.) [<a href="#SSL2">SSL2</a>]</td> - <td>First SSL protocol for which implementations exists</td> - <td>- NS Navigator 1.x/2.x<br /> - - MS IE 3.x<br /> - - Lynx/2.8+OpenSSL</td></tr> - <tr><td>SSL v3.0</td> - <td>Expired Internet Draft (from Netscape Corp.) [<a href="#SSL3">SSL3</a>]</td> - <td>Revisions to prevent specific security attacks, add non-RSA - ciphers, and support for certificate chains</td> - <td>- NS Navigator 2.x/3.x/4.x<br /> - - MS IE 3.x/4.x<br /> - - Lynx/2.8+OpenSSL</td></tr> - <tr><td>TLS v1.0</td> - <td>Proposed Internet Standard (from IETF) [<a href="#TLS1">TLS1</a>]</td> - <td>Revision of SSL 3.0 to update the MAC layer to HMAC, add block - padding for block ciphers, message order standardization and more - alert messages.</td> - <td>- Lynx/2.8+OpenSSL</td></tr> - </table> - - -<p>There are a number of versions of the SSL protocol, as shown in -<a href="#table4">Table 4</a>. As noted there, one of the benefits in -SSL 3.0 is that it adds support of certificate chain loading. This feature -allows a server to pass a server certificate along with issuer certificates -to the browser. Chain loading also permits the browser to validate the -server certificate, even if Certificate Authority certificates are not -installed for the intermediate issuers, since they are included in the -certificate chain. SSL 3.0 is the basis for the Transport Layer Security -[<a href="#TLS1">TLS</a>] protocol standard, currently in development by -the Internet Engineering Task Force (IETF).</p> - -<h3><a name="session" id="session">Session Establishment</a></h3> - - <p>The SSL session is established by following a handshake sequence - between client and server, as shown in <a href="#figure1">Figure 1</a>. This sequence may vary, depending on whether the server - is configured to provide a server certificate or request a client - certificate. Though cases exist where additional handshake steps - are required for management of cipher information, this article - summarizes one common scenario: see the SSL specification for the full - range of possibilities.</p> - - <div class="note"><h3>Note</h3> - <p>Once an SSL session has been established it may be reused, thus - avoiding the performance penalty of repeating the many steps needed - to start a session. For this the server assigns each SSL session a - unique session identifier which is cached in the server and which the - client can use on forthcoming connections to reduce the handshake - (until the session identifer expires in the cache of the server).</p> - </div> - - <p class="figure"> - <img src="../images/ssl_intro_fig1.gif" alt="" width="423" height="327" /><br /> - <a id="figure1" name="figure1"><dfn>Figure 1</dfn></a>: Simplified SSL - Handshake Sequence</p> - - <p>The elements of the handshake sequence, as used by the client and - server, are listed below:</p> - - <ol> - <li>Negotiate the Cipher Suite to be used during data transfer</li> - <li>Establish and share a session key between client and server</li> - <li>Optionally authenticate the server to the client</li> - <li>Optionally authenticate the client to the server</li> - </ol> - - <p>The first step, Cipher Suite Negotiation, allows the client and - server to choose a Cipher Suite supportable by both of them. The SSL3.0 - protocol specification defines 31 Cipher Suites. A Cipher Suite is - defined by the following components:</p> - - <ul> - <li>Key Exchange Method</li> - <li>Cipher for Data Transfer</li> - <li>Message Digest for creating the Message Authentication Code (MAC)</li> - </ul> - - <p>These three elements are described in the sections that follow.</p> - - -<h3><a name="keyexchange" id="keyexchange">Key Exchange Method</a></h3> - - <p>The key exchange method defines how the shared secret symmetric - cryptography key used for application data transfer will be agreed - upon by client and server. SSL 2.0 uses RSA key exchange only, while - SSL 3.0 supports a choice of key exchange algorithms including the - RSA key exchange when certificates are used, and Diffie-Hellman key - exchange for exchanging keys without certificates and without prior - communication between client and server.</p> - - <p>One variable in the choice of key exchange methods is digital - signatures -- whether or not to use them, and if so, what kind of - signatures to use. Signing with a private key provides assurance - against a man-in-the-middle-attack during the information exchange - used in generating the shared key [<a href="#AC96">AC96</a>, p516].</p> - - -<h3><a name="ciphertransfer" id="ciphertransfer">Cipher for Data Transfer</a></h3> - - <p>SSL uses the conventional cryptography algorithm (symmetric - cryptography) described earlier for encrypting messages in a session. - There are nine choices, including the choice to perform no - encryption:</p> - - <ul> - <li>No encryption</li> - <li>Stream Ciphers - <ul> - <li>RC4 with 40-bit keys</li> - <li>RC4 with 128-bit keys</li> - </ul></li> - <li>CBC Block Ciphers - <ul><li>RC2 with 40 bit key</li> - <li>DES with 40 bit key</li> - <li>DES with 56 bit key</li> - <li>Triple-DES with 168 bit key</li> - <li>Idea (128 bit key)</li> - <li>Fortezza (96 bit key)</li> - </ul></li> - </ul> - - <p>Here "CBC" refers to Cipher Block Chaining, which means that a - portion of the previously encrypted cipher text is used in the - encryption of the current block. "DES" refers to the Data Encryption - Standard [<a href="#AC96">AC96</a>, ch12], which has a number of - variants (including DES40 and 3DES_EDE). "Idea" is one of the best - and cryptographically strongest available algorithms, and "RC2" is - a proprietary algorithm from RSA DSI [<a href="#AC96">AC96</a>, - ch13].</p> - - -<h3><a name="digestfuntion" id="digestfuntion">Digest Function</a></h3> - - <p>The choice of digest function determines how a digest is created - from a record unit. SSL supports the following:</p> - - <ul> - <li>No digest (Null choice)</li> - <li>MD5, a 128-bit hash</li> - <li>Secure Hash Algorithm (SHA-1), a 160-bit hash</li> - </ul> - - <p>The message digest is used to create a Message Authentication Code - (MAC) which is encrypted with the message to provide integrity and to - prevent against replay attacks.</p> - - -<h3><a name="handshake" id="handshake">Handshake Sequence Protocol</a></h3> - - <p>The handshake sequence uses three protocols:</p> - - <ul> - <li>The <dfn>SSL Handshake Protocol</dfn> - for performing the client and server SSL session establishment.</li> - <li>The <dfn>SSL Change Cipher Spec Protocol</dfn> for actually - establishing agreement on the Cipher Suite for the session.</li> - <li>The <dfn>SSL Alert Protocol</dfn> for conveying SSL error - messages between client and server.</li> - </ul> - - <p>These protocols, as well as application protocol data, are - encapsulated in the <dfn>SSL Record Protocol</dfn>, as shown in - <a href="#figure2">Figure 2</a>. An encapsulated protocol is - transferred as data by the lower layer protocol, which does not - examine the data. The encapsulated protocol has no knowledge of the - underlying protocol.</p> - - <p class="figure"> - <img src="../images/ssl_intro_fig2.gif" alt="" width="428" height="217" /><br /> - <a id="figure2" name="figure2"><dfn>Figure 2</dfn></a>: SSL Protocol Stack - </p> - - <p>The encapsulation of SSL control protocols by the record protocol - means that if an active session is renegotiated the control protocols - will be transmitted securely. If there were no session before, then - the Null cipher suite is used, which means there is no encryption and - messages have no integrity digests until the session has been - established.</p> - - -<h3><a name="datatransfer" id="datatransfer">Data Transfer</a></h3> - - <p>The SSL Record Protocol, shown in <a href="#figure3">Figure 3</a>, - is used to transfer application and SSL Control data between the - client and server, possibly fragmenting this data into smaller units, - or combining multiple higher level protocol data messages into single - units. It may compress, attach digest signatures, and encrypt these - units before transmitting them using the underlying reliable transport - protocol (Note: currently all major SSL implementations lack support - for compression).</p> - - <p class="figure"> - <img src="../images/ssl_intro_fig3.gif" alt="" width="423" height="323" /><br /> - <a id="figure3" name="figure3"><dfn>Figure 3</dfn></a>: SSL Record Protocol - </p> - - -<h3><a name="securehttp" id="securehttp">Securing HTTP Communication</a></h3> - - <p>One common use of SSL is to secure Web HTTP communication between - a browser and a webserver. This case does not preclude the use of - non-secured HTTP. The secure version is mainly plain HTTP over SSL - (named HTTPS), but with one major difference: it uses the URL scheme - <code>https</code> rather than <code>http</code> and a different - server port (by default 443). This mainly is what <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> provides to you for the Apache webserver...</p> - -</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="references" id="references">References</a></h2> - -<dl> -<dt><a id="AC96" name="AC96">[AC96]</a></dt> -<dd>Bruce Schneier, <q>Applied Cryptography</q>, 2nd Edition, Wiley, -1996. See <a href="http://www.counterpane.com/">http://www.counterpane.com/</a> for various other materials by Bruce -Schneier.</dd> - -<dt><a id="X208" name="X208">[X208]</a></dt> -<dd>ITU-T Recommendation X.208, <q>Specification of Abstract Syntax Notation -One (ASN.1)</q>, 1988. See for instance <a href="http://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=T-REC-X.208-198811-I">http://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=T-REC-X.208-198811-I</a>. -</dd> - -<dt><a id="X509" name="X509">[X509]</a></dt> -<dd>ITU-T Recommendation X.509, <q>The Directory - Authentication -Framework</q>. See for instance <a href="http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-X.509">http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-X.509</a>. -</dd> - -<dt><a id="PKCS" name="PKCS">[PKCS]</a></dt> -<dd><q>Public Key Cryptography Standards (PKCS)</q>, -RSA Laboratories Technical Notes, See <a href="http://www.rsasecurity.com/rsalabs/pkcs/">http://www.rsasecurity.com/rsalabs/pkcs/</a>.</dd> - -<dt><a id="MIME" name="MIME">[MIME]</a></dt> -<dd>N. Freed, N. Borenstein, <q>Multipurpose Internet Mail Extensions -(MIME) Part One: Format of Internet Message Bodies</q>, RFC2045. -See for instance <a href="http://ietf.org/rfc/rfc2045.txt">http://ietf.org/rfc/rfc2045.txt</a>.</dd> - -<dt><a id="SSL2" name="SSL2">[SSL2]</a></dt> -<dd>Kipp E.B. Hickman, <q>The SSL Protocol</q>, 1995. See <a href="http://www.netscape.com/eng/security/SSL_2.html">http://www.netscape.com/eng/security/SSL_2.html</a>.</dd> - -<dt><a id="SSL3" name="SSL3">[SSL3]</a></dt> -<dd>Alan O. Freier, Philip Karlton, Paul C. Kocher, <q>The SSL Protocol -Version 3.0</q>, 1996. See <a href="http://www.netscape.com/eng/ssl3/draft302.txt">http://www.netscape.com/eng/ssl3/draft302.txt</a>.</dd> - -<dt><a id="TLS1" name="TLS1">[TLS1]</a></dt> -<dd>Tim Dierks, Christopher Allen, <q>The TLS Protocol Version 1.0</q>, -1999. See <a href="http://ietf.org/rfc/rfc2246.txt">http://ietf.org/rfc/rfc2246.txt</a>.</dd> -</dl> -</div></div> -<div class="bottomlang"> -<p><span>Available Languages: </span><a href="../en/ssl/ssl_intro.html" title="English"> en </a> | -<a href="../ja/ssl/ssl_intro.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p> -</div><div id="footer"> -<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> -<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div> -</body></html>
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