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455 lines
20 KiB
HTML
455 lines
20 KiB
HTML
<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
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"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"[
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<!ENTITY % brandDTD SYSTEM "chrome://branding/locale/brand.dtd" >
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%brandDTD;
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]>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>Signing & Encrypting Messages</title>
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<link rel="stylesheet" href="chrome://help/locale/helpFileLayout.css"
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type="text/css"/>
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</head>
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<body>
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<h1 id="signing_and_encrypting_messages">Signing & Encrypting Messages</h1>
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<div class="contentsBox">In this section:
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<ul>
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<li><a href="#about_digital_signatures_and_encryption">About Digital
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Signatures & Encryption</a></li>
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<li><a href="#getting_other_peoples_certificates">Getting Other
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People's Certificates</a></li>
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<li><a href="#configuring_security_settings">Configuring Security
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Settings</a></li>
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<li><a href="#signing_and_encrypting_a_new_message">Signing &
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Encrypting a New Message</a></li>
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<li><a href="#reading_signed_and_encrypted_messages">Reading Signed &
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Encrypted Messages</a></li>
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<li><a href="#message_security_compose_window">Message Security -
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Compose Window</a></li>
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<li><a href="#message_security_recieved_message">Message Security -
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Received Message</a></li>
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</ul>
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</div>
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<h2 id="about_digital_signatures_and_encryption">About Digital Signatures &
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Encryption </h2>
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<p>When you compose a mail message, you can choose to attach your digital
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signature to it. A <a href="glossary.xhtml#digital_signature">digital
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signature</a> allows recipients of the message to verify that the message
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really comes from you and hasn't been tampered with since you sent
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it.</p>
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<p>When you compose a mail message, you can also choose to encrypt it.
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<a href="glossary.xhtml#encryption">Encryption</a> makes it very difficult
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for anyone other than the intended recipient to read the message while it is
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in transit over the Internet.</p>
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<p>Signing and encryption are not available for newsgroup messages.</p>
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<p>Before you can sign or encrypt a message, you must take these preliminary
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steps:</p>
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<ol>
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<li>Obtain one or more <a href="glossary.xhtml#certificate">certificates</a>
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(the digital equivalents of ID cards). For details, see
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<a href="using_certs_help.xhtml#getting_your_own_certificate">Getting Your
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Own Certificate</a>.</li>
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<li>Configure the security settings for your email account. For details, see
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<a href="mail_help.xhtml#security">Configuring Your Security Settings</a>.
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</li>
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</ol>
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<p>Once you have completed these steps, you can complete the instructions in
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<a href="#signing_and_encrypting_a_new_message">Signing & Encrypting a
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New Message</a>.</p>
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<p>The sections that follow provide a brief overview of how digital signatures
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and encryption work. For more technical details on this subject, see the
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online document
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<a href="http://developer.mozilla.org/en/docs/Introduction_to_Public-Key_Cryptography">Introduction
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to Public-Key Cryptography</a>.</p>
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<h3 id="how_digital_signatures_work">How Digital Signatures Work</h3>
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<p>A digital signature is a special code, unique to each message, created by
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means of <a href="glossary.xhtml#public-key_cryptography">public-key
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cryptography</a>.</p>
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<p>A digital signature is completely different from a handwritten signature,
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although it can sometimes be used for similar legal purposes, such as signing
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a contract.</p>
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<p>To create a digital signature for an email message that you are sending, you
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need two things:</p>
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<ul>
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<li>A <a href="glossary.xhtml#signing_certificate">signing certificate</a>
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that identifies you for this purpose. Every time you sign a message, your
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signing certificate is included with the message. The certificate includes
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a <a href="glossary.xhtml#public_key">public key</a>. The presence of the
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certificate in the message permits the recipient to verify your digital
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signature.
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<p>Your certificate is a bit like your name and phone number in the
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phonebook—it is public information that helps other people
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communicate with you.</p>
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</li>
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<li>A <a href="glossary.xhtml#private_key">private key</a>, which is created
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and stored on your computer when you first obtain a certificate.
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<p>Your private key for a signing certificate is protected by your
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<a href="glossary.xhtml#master_password">Master Password</a>, and the
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&brandShortName; program does not disclose it to anyone else. The Mail
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& Newsgroup software uses your private key to create a unique,
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verifiable digital signature for every message you choose to sign.</p>
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</li>
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</ul>
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<h3 id="how_encryption_works">How Encryption Works</h3>
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<p>To encrypt an email message, you must have an
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<a href="glossary.xhtml#encryption_certificate">encryption certificate</a>
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for each of the message's recipients. The public key in each certificate
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is used to encrypt the message for that recipient.</p>
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<p>If you don't have a certificate for even a single recipient, the
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message cannot be encrypted.</p>
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<p>The recipient's software uses the recipient's private key, which
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remains on that person's computer, to decrypt the message.</p>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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<h2 id="getting_other_peoples_certificates">Getting Other People's
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Certificates</h2>
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<p>Every time you send a digitally signed message, your encryption certificate
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is automatically included with the message. Therefore, one of the easiest
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ways to obtain someone else's certificate is for that person to send you
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a digitally signed message.</p>
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<p>When you receive such a message, the person's certificate is
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automatically stored by the <a href="certs_help.xhtml">Certificate
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Manager</a>, which is the part of the browser that keeps track of
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certificates. This is useful because you need to have a certificate for each
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recipient of any email message that you want to send in encrypted form.</p>
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<p>Another way to obtain certificates is to look them up in a public directory,
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such as the <q>phonebook</q> directories maintained by many companies.</p>
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<p>It's also possible to look up certificates automatically. This feature
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is controlled by <a href="mail_help.xhtml#addressing_preferences">Mail &
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Newsgroups Preferences - Addressing</a> or
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<a href="mail_help.xhtml#addressing">Mail & Newsgroups Account Settings -
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Addressing</a>, which can be configured to look up recipients' email
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addresses in a directory.</p>
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<p>When you are using any account that is configured to look up addresses in a
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directory, the same directory will be searched for matching certificates when
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you attempt to send an encrypted message to one or more recipients for whom
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you don't have certificates on file.</p>
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<p>The directory will also be searched for missing certificates when you open
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the drop-down menu below the Security icon in the Compose window and choose
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View Security Info.</p>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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<h2 id="configuring_security_settings">Configuring Security Settings</h2>
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<p>Once you have obtained an email certificate (or certificates), you must
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specify the certificates you want to use for signing and encrypting
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messages.</p>
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<p>For information about obtaining email certificates, see
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<a href="using_certs_help.xhtml#getting_your_own_certificate">Getting Your
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Own Certificate</a>.</p>
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<p>To specify which signing and encryption certificates to use with a
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particular account, begin from the Mail window:</p>
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<ol>
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<li>Open the Edit menu and choose Mail & Newsgroups Account Settings.</li>
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<li>Click Security under the name of the mail account whose security settings
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you want to configure.</li>
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<li>Under Digital Signing, click Select. (You may be asked to provide your
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<a href="glossary.xhtml#master_password">Master Password</a> before you can
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proceed further.)
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<p>A dialog box appears that allows you to select from among your available
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signing certificates.</p>
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</li>
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<li>Choose the signing certificate you want to use, then click OK.</li>
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<li>Follow the same steps under Encryption: click the Select button, select
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the encryption certificate you want to use, and click OK.</li>
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<p>In some cases you may be able to specify the same certificate under
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Encryption that you specified under Digital Signing; check with your system
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administrator to find out for sure.</p>
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</ol>
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<p>Optionally, you can also indicate that you normally want to sign or encrypt
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all messages sent from a particular account. These account-specific settings
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are for convenience only; you can override the default settings for
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individual messages.</p>
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<p>To configure your default signing and encryption settings, start from the
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Security panel for the account (described above) and select your settings as
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follows:</p>
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<ul>
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<li>Under Digital Signing:
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<ul>
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<li><strong>Digitally sign messages</strong>: When this checkbox is
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selected, all the messages you send from this account will be digitally
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signed unless you indicate otherwise before you send the message. To
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turn off this default setting, deselect the checkbox.</li>
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</ul>
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</li>
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<li>Under Encryption (choose one):
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<ul>
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<li><strong>Never</strong>: When this option is selected, messages you
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send from this account will be not be encrypted unless you indicate
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otherwise before you send them.</li>
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<li><strong>Required</strong>: When this option is selected, all the
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messages you send from this account will be encrypted—but only if
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you have valid certificates for each of the message's recipients.
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If you don't have all the necessary certificates, the message
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can't be sent unless you turn off encryption for that message.</li>
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</ul>
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</li>
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</ul>
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<p>When you have finished configuring your mail security settings, click OK to
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confirm them.</p>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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<h2 id="signing_and_encrypting_a_new_message">Signing & Encrypting a New
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Message</h2>
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<p>Before you can digitally sign or encrypt any message, you must obtain at
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least one email certificate and configure your mail security settings
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correctly. For background information on these tasks, see
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<a href="#about_digital_signatures_and_encryption">About Digital Signatures
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& Encryption</a>.</p>
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<p>The settings specified in <a href="mail_help.xhtml#security">Mail &
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Newsgroups Account Settings - Security</a> determine the default settings for
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each new Compose window you open when you set out to write an email.</p>
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<p>To open a Compose window, start from the Mail window and click Compose. You
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can immediately identify the default security settings from the presence or
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absence of these icons near the lower-right corner of the window:</p>
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<table>
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<tr>
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<td><img src="chrome://messenger/skin/smime/icons/hdrSignOk.gif"
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alt="digital signature icon"/></td><td>The message will be digitally
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signed (assuming you have a valid email certificate that
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identifies you).</td>
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</tr>
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<tr>
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<td><img src="chrome://messenger/skin/smime/icons/hdrCryptoOk.gif"
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alt="encryption icon"/></td><td>The message will be encrypted
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(assuming you have valid certificates for all recipients).</td>
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</tr>
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</table>
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<p>To turn these settings off or on, click the arrow just below the Security
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icon in the Mail toolbar near the top of the window. Then select the item you
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want from the drop-down list:</p>
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<ul>
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<li><strong>Do Not Encrypt This Message</strong>: Choose this to turn off
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encryption for this message. The message will not be encrypted when it is
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sent over the Internet.</li>
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<li><strong>Encrypt This Message</strong>: Choose this to turn on encryption
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for this message. The message will be sent in encrypted form. However, it
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can't be sent unless you have valid certificates for all
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recipients.</li>
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<li><strong>Digitally Sign This Message</strong>: Choose this to turn digital
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signing on or off for this message. A checkmark indicates the message will
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be signed.</li>
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<li><strong>View Security Info</strong>: Choose this to view detailed
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information about the security status of this message—to help you
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determine, for example, whether you need to obtain a certificate for one of
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the recipients.</li>
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</ul>
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<p>To view detailed information about the message's security status, you
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can also click the key or lock icon as described in
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<a href="#message_security_compose_window">Message Security - Compose
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Window</a>.</p>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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<h2 id="reading_signed_and_encrypted_messages">Reading Signed & Encrypted
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Messages</h2>
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<p>When you view a signed or encrypted message in the Mail window, these icons
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near the upper-right corner of the message header indicate the security
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status of the message:</p>
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<table>
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<tr>
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<td><img src="chrome://messenger/skin/smime/icons/hdrSignOk.gif"
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alt="digital signature icon"/></td><td>The message is digitally
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signed and has been validated. If there is a problem with the signature,
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the pen is broken.</td>
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</tr>
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<tr>
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<td><img src="chrome://messenger/skin/smime/icons/hdrSignUnknown.gif"
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alt="unknown icon"/></td><td>The message is signed, but it has a
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large attachment that has not yet been downloaded from the IMAP server.
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As a result, the signature cannot be validated. Click the icon to
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download the attachment and validate the signature.</td>
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</tr>
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<tr>
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<td><img src="chrome://messenger/skin/smime/icons/hdrCryptoOk.gif"
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alt="encryption icon"/></td><td>The message is encrypted. If there
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is a problem with the encryption, the key is broken.</td>
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</tr>
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</table>
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<p>For information about certificate validation, see
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<a href="using_certs_help.xhtml#controlling_validation">Controlling
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Validation</a>.</p>
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<p>To see more detailed information about the message's security, click
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the key or lock icon, or follow the instructions in
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<a href="#message_security_recieved_message">Message Security - Received
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Message</a>.</p>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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<h2 id="message_security_compose_window">Message Security - Compose Window</h2>
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<p>This section describes the Message Security window that you can open for any
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message you are composing. If you're not already viewing Message
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Security, click the Security icon in the toolbar of the Compose window.</p>
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<p>The Message Security window describes how your message will be sent:</p>
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<ul>
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<li><strong>Digitally Signed</strong>: This line describes whether your
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message will be signed. There are three possibilities:
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<ul>
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<li><strong>Yes</strong>: Digital signing has been enabled for this
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message, you have a valid certificate identifying you, and the message
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can be signed.</li>
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<li><strong>No</strong>: Digital signing has been disabled for this
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message.</li>
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<li><strong>Not possible</strong>: Digital signing has been enabled for
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this message. However, a valid
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<a href="glossary.xhtml#certificate">certificate</a> identifying you
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for this purpose is not available, or there is some other problem that
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makes signing impossible.</li>
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</ul>
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</li>
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<li><strong>Encrypted</strong>: This line describes whether your message will
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be encrypted. There are three possibilities:
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<ul>
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<li><strong>Yes</strong>: Encryption has been enabled for this message,
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valid certificates for all listed recipients are available, and the
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message can be encrypted.</li>
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<li><strong>No</strong>: Encryption has been disabled or is not possible
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for this message.</li>
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<li><strong>Not possible</strong>: Encryption has been enabled for this
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message. However, a valid certificate for at least one of the listed
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recipients is not available, or no recipients are listed, or there is
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some other problem that makes encryption impossible.</li>
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</ul>
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</li>
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</ul>
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<p>The Message Security window also lists the certificates available for the
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recipients of your message:</p>
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<ul>
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<li><strong>View</strong>: To view the details for any certificate in the
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list, select its name, then click View.</li>
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</ul>
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<p>For more information about obtaining certificates and configuring message
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security settings, see <a href="#signing_and_encrypting_messages">Signing
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& Encrypting Messages</a>.</p>
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<p>To indicate your signing or encryption choices for an individual message,
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click the arrow beside the Security button in the Compose window, then select
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the options you want.</p>
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<p>To indicate your default signing and encryption preferences for all
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messages, see <a href="mail_help.xhtml#security">Mail & Newsgroups
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Account Settings - Security</a></p>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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<h2 id="message_security_recieved_message">Message Security - Received
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Message</h2>
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<p>This section describes the Message Security window that you can open for any
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message you have received. If you're not already viewing Message
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Security for a received message, follow these steps:</p>
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<ol>
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<li>In the Mail window, select the message for which you want to view
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security information.</li>
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<li>Open the View menu and choose Message Security Info.</li>
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</ol>
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<p>The Message Security window displays the following information:</p>
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<ul>
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<li><strong>Digital Signature</strong>: The top section describes whether the
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message is digitally signed and if so, whether the signature is valid.</li>
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<p>If validation failed while OCSP was enabled, check the OCSP settings in
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<a href="validation_help.xhtml#privacy_and_security_preferences_validation">Privacy
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& Security Preferences - Validation</a>. If you are not familiar with
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OCSP, confirm the settings with your system administrator. If your settings
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are correct, there may be a problem with the OCSP service or the
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certificate used to create the signature is no longer valid.</p>
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<p>If the signature is invalid because of a problem with a certificate's
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trust settings, you can use the <a href="certs_help.xhtml">Certificate
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Manager</a> to view or edit those settings.</p>
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<li><strong>View Signature Certificate</strong>: If the message is signed,
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click this button to view the certificate that was used to sign it.</li>
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<li><strong>Encryption</strong>: The bottom section reports whether the
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message is encrypted and any decrypting problems.
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<ul>
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<li>If the message's contents have been altered during transit, you
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should ask the sender to resend it. The changes may have been caused by
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network problems.</li>
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<li>If a copy of your own certificate (used by the sender to encrypt the
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message) is not available on your computer, the private key required to
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decrypt the message cannot be retrieved. The only solution is to import
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a backup copy of your certificate and its private key (see
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<a href="certs_help.xhtml#your_certificates">Your Certificates</a> for
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details.) If you don't have access to a backup certificate, you
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will not be able to decrypt the message.</li>
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</ul>
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</li>
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</ul>
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<p>[<a href="#signing_and_encrypting_messages">Return to beginning of
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section</a>]</p>
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|
<p>Copyright © 2003-2010 The Mozilla Foundation.</p>
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</body>
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</html>
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