293 lines
14 KiB
HTML
293 lines
14 KiB
HTML
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8"/>
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<style>
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table.head, table.foot { width: 100%; }
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td.head-rtitle, td.foot-os { text-align: right; }
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td.head-vol { text-align: center; }
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div.Pp { margin: 1ex 0ex; }
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</style>
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<link rel="stylesheet" href="style.css" type="text/css" media="all"/>
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<title>CRYPTO_LOCK(3MONOCYPHER)</title>
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</head>
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<body>
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<table class="head">
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<tr>
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<td class="head-ltitle">CRYPTO_LOCK(3MONOCYPHER)</td>
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<td class="head-vol">3MONOCYPHER</td>
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<td class="head-rtitle">CRYPTO_LOCK(3MONOCYPHER)</td>
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</tr>
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</table>
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<div class="manual-text">
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<h1 class="Sh" title="Sh" id="NAME"><a class="selflink" href="#NAME">NAME</a></h1>
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<b class="Nm" title="Nm">crypto_aead_lock</b>,
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<b class="Nm" title="Nm">crypto_aead_unlock</b>,
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<b class="Nm" title="Nm">crypto_lock</b>,
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<b class="Nm" title="Nm">crypto_unlock</b> —
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<span class="Nd" title="Nd">authenticated encryption with additional
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data</span>
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<h1 class="Sh" title="Sh" id="SYNOPSIS"><a class="selflink" href="#SYNOPSIS">SYNOPSIS</a></h1>
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<b class="In" title="In">#include
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<<a class="In" title="In">monocypher.h</a>></b>
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<div class="Pp"></div>
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<var class="Ft" title="Ft">void</var>
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<br/>
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<b class="Fn" title="Fn">crypto_lock</b>(<var class="Fa" title="Fa">uint8_t
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mac[16]</var>, <var class="Fa" title="Fa">uint8_t *cipher_text</var>,
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<var class="Fa" title="Fa">const uint8_t key[32]</var>,
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<var class="Fa" title="Fa">const uint8_t nonce[24]</var>,
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<var class="Fa" title="Fa">const uint8_t *plain_text</var>,
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<var class="Fa" title="Fa">size_t text_size</var>);
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<div class="Pp"></div>
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<var class="Ft" title="Ft">int</var>
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<br/>
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<b class="Fn" title="Fn">crypto_unlock</b>(<var class="Fa" title="Fa">uint8_t
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*plain_text</var>, <var class="Fa" title="Fa">const uint8_t key[32]</var>,
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<var class="Fa" title="Fa">const uint8_t nonce[24]</var>,
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<var class="Fa" title="Fa">const uint8_t mac[16]</var>,
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<var class="Fa" title="Fa">const uint8_t *cipher_text</var>,
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<var class="Fa" title="Fa">size_t text_size</var>);
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<div class="Pp"></div>
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<var class="Ft" title="Ft">void</var>
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<br/>
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<b class="Fn" title="Fn">crypto_aead_lock</b>(<var class="Fa" title="Fa">uint8_t
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mac[16]</var>, <var class="Fa" title="Fa">uint8_t *cipher_text</var>,
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<var class="Fa" title="Fa">const uint8_t key[32]</var>,
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<var class="Fa" title="Fa">const uint8_t nonce[24]</var>,
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<var class="Fa" title="Fa">const uint8_t *ad</var>,
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<var class="Fa" title="Fa">size_t ad_size</var>,
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<var class="Fa" title="Fa">const uint8_t *plain_text</var>,
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<var class="Fa" title="Fa">size_t text_size</var>);
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<div class="Pp"></div>
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<var class="Ft" title="Ft">int</var>
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<br/>
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<b class="Fn" title="Fn">crypto_aead_unlock</b>(<var class="Fa" title="Fa">uint8_t
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*plain_text</var>, <var class="Fa" title="Fa">const uint8_t key[32]</var>,
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<var class="Fa" title="Fa">const uint8_t nonce[24]</var>,
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<var class="Fa" title="Fa">const uint8_t mac[16]</var>,
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<var class="Fa" title="Fa">const uint8_t *ad</var>,
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<var class="Fa" title="Fa">size_t ad_size</var>,
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<var class="Fa" title="Fa">const uint8_t *cipher_text</var>,
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<var class="Fa" title="Fa">size_t text_size</var>);
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<h1 class="Sh" title="Sh" id="DESCRIPTION"><a class="selflink" href="#DESCRIPTION">DESCRIPTION</a></h1>
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<b class="Fn" title="Fn">crypto_lock</b>() encrypts and authenticates a
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plaintext. It can be decrypted by
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<b class="Fn" title="Fn">crypto_unlock</b>(). The arguments are:
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<dl class="Bl-tag">
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">key</var></dt>
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<dd class="It-tag">A 32-byte session key, shared between the sender and the
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recipient. It must be secret and random. Different methods can be used to
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produce and exchange this key, such as Diffie-Hellman key exchange,
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password key derivation (the password must be communicated on a secure
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channel), or even meeting physically. See
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<a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>
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for key exchange, and
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<a class="Xr" title="Xr" href="crypto_argon2i.html">crypto_argon2i(3monocypher)</a>
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for password key derivation.</dd>
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">nonce</var></dt>
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<dd class="It-tag">A 24-byte number, used only once with any given session
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key. It does not need to be secret or random, but it does have to be
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unique. <i class="Em" title="Em">Never</i> use the same nonce twice with
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the same key. This would reveal the XOR of 2 different messages, which
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allows decryption and forgeries. The easiest (and recommended) way to
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generate this nonce is to select it at random. See
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<a class="Xr" title="Xr" href="intro.html">intro(3monocypher)</a> about
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random number generation (use your operating system's random number
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generator).</dd>
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">mac</var></dt>
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<dd class="It-tag">A 16-byte <i class="Em" title="Em">message authentication
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code</i> (MAC), that can only be produced by someone who knows the session
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key. This guarantee cannot be upheld if a nonce has been reused with the
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session key, because doing so allows the attacker to learn the
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authentication key associated with that nonce. The MAC is intended to be
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sent along with the ciphertext.</dd>
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">plain_text</var></dt>
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<dd class="It-tag">The secret message. Its contents will be kept hidden from
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attackers. Its length however, will <i class="Em" title="Em">not</i>. Be
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careful when combining encryption with compression. See
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<a class="Xr" title="Xr" href="intro.html">intro(3monocypher)</a> for
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details.</dd>
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">cipher_text</var></dt>
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<dd class="It-tag">The encrypted message.</dd>
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">text_size</var></dt>
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<dd class="It-tag">Length of both <var class="Fa" title="Fa">plain_text
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and</var> <var class="Fa" title="Fa">cipher_text</var>, in bytes.</dd>
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</dl>
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<div class="Pp"></div>
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The <var class="Fa" title="Fa">cipher_text</var> and
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<var class="Fa" title="Fa">plain_text</var> arguments may point to the same
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buffer for in-place encryption. Otherwise, the buffers they point to must not
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overlap.
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<div class="Pp"></div>
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<b class="Fn" title="Fn">crypto_unlock</b>() first checks the integrity of an
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encrypted message. If it has been corrupted,
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<b class="Fn" title="Fn">crypto_unlock</b>() returns -1 immediately.
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Otherwise, it decrypts the message, then returns zero.
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<i class="Em" title="Em">Always check the return value</i>.
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<div class="Pp"></div>
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<b class="Fn" title="Fn">crypto_aead_lock</b>() and
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<b class="Fn" title="Fn">crypto_aead_unlock</b>() are variants of
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<b class="Fn" title="Fn">crypto_lock</b>() and
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<b class="Fn" title="Fn">crypto_unlock</b>(), permitting additional data.
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Additional data is authenticated, but <i class="Em" title="Em">not</i>
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encrypted. This is used to authenticate relevant data that cannot be
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encrypted. The arguments are:
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<dl class="Bl-tag">
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">ad</var></dt>
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<dd class="It-tag">Additional data to authenticate. It will not be encrypted.
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May be <code class="Dv" title="Dv">NULL</code> if
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<var class="Fa" title="Fa">ad_size</var> is zero. Setting
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<var class="Fa" title="Fa">ad_size</var> to zero yields the same results
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as <b class="Fn" title="Fn">crypto_lock</b>() and
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<b class="Fn" title="Fn">crypto_unlock</b>().</dd>
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<dt class="It-tag"> </dt>
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<dd class="It-tag"> </dd>
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<dt class="It-tag"><var class="Fa" title="Fa">ad_size</var></dt>
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<dd class="It-tag">Length of the additional data, in bytes.
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<b class="Sy" title="Sy">That length is not authenticated.</b> If the
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additional data is of variable length, the length should be appended to
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<var class="Fa" title="Fa">ad</var> so it gets authenticated, and should
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be extracted from the end of the message when decrypting. Otherwise an
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attacker could provide a false length, effectively moving the boundary
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between the additional data and the ciphertext. This may cause buffer
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overflows in some programs.</dd>
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</dl>
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<div class="Pp"></div>
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An incremental interface is available; see
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<a class="Xr" title="Xr" href="crypto_lock_init.html">crypto_lock_init(3monocypher)</a>.
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<h1 class="Sh" title="Sh" id="RETURN_VALUES"><a class="selflink" href="#RETURN_VALUES">RETURN
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VALUES</a></h1>
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<b class="Fn" title="Fn">crypto_lock</b>() and
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<b class="Fn" title="Fn">crypto_aead_lock</b>() return nothing. They cannot
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fail. <b class="Fn" title="Fn">crypto_unlock</b>() and
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<b class="Fn" title="Fn">crypto_aead_unlock</b>() return 0 on success or -1 if
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the message was corrupted (i.e. <var class="Fa" title="Fa">mac</var>
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mismatched the combination of <var class="Fa" title="Fa">key</var>,
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<var class="Fa" title="Fa">nonce</var>, <var class="Fa" title="Fa">ad</var>
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and <var class="Fa" title="Fa">cipher_text</var>). Corruption can be caused by
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transmission errors, programmer error, or an attacker's interference.
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<var class="Fa" title="Fa">plain_text</var> does not need to be wiped if the
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decryption fails.
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<h1 class="Sh" title="Sh" id="EXAMPLES"><a class="selflink" href="#EXAMPLES">EXAMPLES</a></h1>
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Encryption:
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<div class="Pp"></div>
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<div class="Bd" style="margin-left: 5.00ex;">
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<pre class="Li">
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const uint8_t key [32]; /* Random, secret session key */
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const uint8_t nonce [24]; /* Use only once per key */
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const uint8_t plain_text [500]; /* Secret message */
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uint8_t mac [16]; /* Message authentication code */
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uint8_t cipher_text[500]; /* Encrypted message */
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crypto_lock(mac, cipher_text, key, nonce, plain_text, 500);
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/* Wipe secrets if they are no longer needed */
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crypto_wipe(plain_text, 500);
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crypto_wipe(key, 32);
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/* Transmit cipher_text, nonce, and mac over the network */
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</pre>
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</div>
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<div class="Pp"></div>
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To decrypt the above:
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<div class="Pp"></div>
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<div class="Bd" style="margin-left: 5.00ex;">
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<pre class="Li">
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const uint8_t key [32]; /* Same as the above */
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const uint8_t nonce [24]; /* Same as the above */
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const uint8_t cipher_text[500]; /* Encrypted message */
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const uint8_t mac [16]; /* Received from the network */
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uint8_t plain_text [500]; /* Secret message */
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if (crypto_unlock(plain_text, key, nonce, mac, cipher_text, 500)) {
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/* The message is corrupted.
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* Wipe key if it is no longer needed,
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* and abort the decryption.
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*/
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crypto_wipe(key, 32);
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}
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/* Wipe secrets if they are no longer needed */
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crypto_wipe(plain_text, 500);
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crypto_wipe(key, 32);
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</pre>
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</div>
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<div class="Pp"></div>
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In-place encryption:
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<div class="Pp"></div>
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<div class="Bd" style="margin-left: 5.00ex;">
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<pre class="Li">
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const uint8_t key [32]; /* Random, secret session key */
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const uint8_t nonce[24]; /* Use only once per key */
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uint8_t text [500]; /* Secret message */
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uint8_t mac [16]; /* Message authentication code */
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crypto_lock(mac, text, key, nonce, text, 500);
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/* Wipe secrets if they are no longer needed */
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crypto_wipe(key, 32);
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/* Transmit text, nonce, and mac over the network */
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</pre>
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</div>
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<div class="Pp"></div>
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In-place decryption:
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<div class="Pp"></div>
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<div class="Bd" style="margin-left: 5.00ex;">
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<pre class="Li">
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const uint8_t key [32]; /* Same as the above */
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const uint8_t nonce[24]; /* Same as the above */
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const uint8_t mac [16]; /* Reived from the network */
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uint8_t text [500]; /* Message to decrypt */
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if (crypto_unlock(text, key, nonce, mac, text, 500)) {
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/* The message is corrupted.
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* Wipe key if it is no longer needed,
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* and abort the decryption.
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*/
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crypto_wipe(key, 32);
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}
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/* Wipe secrets if they are no longer needed */
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crypto_wipe(text, 500);
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crypto_wipe(key, 32);
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</pre>
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</div>
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<h1 class="Sh" title="Sh" id="SEE_ALSO"><a class="selflink" href="#SEE_ALSO">SEE
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ALSO</a></h1>
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<a class="Xr" title="Xr" href="crypto_key_exchange.html">crypto_key_exchange(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_lock_init.html">crypto_lock_init(3monocypher)</a>,
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<a class="Xr" title="Xr" href="crypto_wipe.html">crypto_wipe(3monocypher)</a>,
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<a class="Xr" title="Xr" href="intro.html">intro(3monocypher)</a>
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<h1 class="Sh" title="Sh" id="STANDARDS"><a class="selflink" href="#STANDARDS">STANDARDS</a></h1>
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These functions implement the XChacha20 (encryption) and Poly1305 (MAC)
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primitives. Chacha20 and Poly1305 are described in RFC 7539. XChacha20 derives
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from Chacha20 the same way XSalsa20 derives from Salsa20, and benefits from
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the same security reduction (proven secure as long as Chacha20 itself is
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secure).
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<h1 class="Sh" title="Sh" id="IMPLEMENTATION_DETAILS"><a class="selflink" href="#IMPLEMENTATION_DETAILS">IMPLEMENTATION
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DETAILS</a></h1>
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<b class="Fn" title="Fn">crypto_aead_lock</b>() and
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<b class="Fn" title="Fn">crypto_aead_unlock</b>() do not authenticate the
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length themselves to make them compatible with
|
||
|
|
<b class="Fn" title="Fn">crypto_lock</b>() and
|
||
|
|
<b class="Fn" title="Fn">crypto_unlock</b>() when the size of the additional
|
||
|
|
data is zero. This also simplifies the implementation.
|
||
|
|
<div class="Pp"></div>
|
||
|
|
This rarely causes problems in practice, because most of the time, the length of
|
||
|
|
the additional data is either fixed or self-contained, and thus outside of
|
||
|
|
attacker control.</div>
|
||
|
|
<table class="foot">
|
||
|
|
<tr>
|
||
|
|
<td class="foot-date">December 28, 2017</td>
|
||
|
|
<td class="foot-os">Linux 4.4.0-116-generic</td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
</body>
|
||
|
|
</html>
|