2020-03-02 11:50:34 -05:00
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<title>EVP_SealInit</title>
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<!-- INDEX BEGIN -->
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<div name="index">
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<p><a name="__index__"></a></p>
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<ul>
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<li><a href="#name">NAME</a></li>
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<li><a href="#synopsis">SYNOPSIS</a></li>
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<li><a href="#description">DESCRIPTION</a></li>
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<li><a href="#return_values">RETURN VALUES</a></li>
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<li><a href="#notes">NOTES</a></li>
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<li><a href="#see_also">SEE ALSO</a></li>
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<li><a href="#copyright">COPYRIGHT</a></li>
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<p>
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</p>
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<h1><a name="name">NAME</a></h1>
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<p>EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption</p>
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<p>
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</p>
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<hr />
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<h1><a name="synopsis">SYNOPSIS</a></h1>
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<pre>
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#include <openssl/evp.h></pre>
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<pre>
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int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
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unsigned char **ek, int *ekl, unsigned char *iv,
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EVP_PKEY **pubk, int npubk);
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int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);</pre>
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<p>
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</p>
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<hr />
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<h1><a name="description">DESCRIPTION</a></h1>
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<p>The EVP envelope routines are a high level interface to envelope
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encryption. They generate a random key and IV (if required) then
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"envelope" it by using public key encryption. Data can then be
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encrypted using this key.</p>
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<p><code>EVP_SealInit()</code> initializes a cipher context <strong>ctx</strong> for encryption
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with cipher <strong>type</strong> using a random secret key and IV. <strong>type</strong> is normally
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supplied by a function such as EVP_aes_256_cbc(). The secret key is encrypted
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using one or more public keys, this allows the same encrypted data to be
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decrypted using any of the corresponding private keys. <strong>ek</strong> is an array of
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buffers where the public key encrypted secret key will be written, each buffer
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must contain enough room for the corresponding encrypted key: that is
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<strong>ek[i]</strong> must have room for <strong>EVP_PKEY_size(pubk[i])</strong> bytes. The actual
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size of each encrypted secret key is written to the array <strong>ekl</strong>. <strong>pubk</strong> is
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an array of <strong>npubk</strong> public keys.</p>
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<p>The <strong>iv</strong> parameter is a buffer where the generated IV is written to. It must
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contain enough room for the corresponding cipher's IV, as determined by (for
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example) EVP_CIPHER_iv_length(type).</p>
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<p>If the cipher does not require an IV then the <strong>iv</strong> parameter is ignored
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and can be <strong>NULL</strong>.</p>
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<p><code>EVP_SealUpdate()</code> and <code>EVP_SealFinal()</code> have exactly the same properties
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as the <code>EVP_EncryptUpdate()</code> and <code>EVP_EncryptFinal()</code> routines, as
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documented on the <em>EVP_EncryptInit(3)</em> manual
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page.</p>
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<p>
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</p>
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<hr />
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<h1><a name="return_values">RETURN VALUES</a></h1>
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<p><code>EVP_SealInit()</code> returns 0 on error or <strong>npubk</strong> if successful.</p>
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<p><code>EVP_SealUpdate()</code> and <code>EVP_SealFinal()</code> return 1 for success and 0 for
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failure.</p>
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<p>
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</p>
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<hr />
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<h1><a name="notes">NOTES</a></h1>
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<p>Because a random secret key is generated the random number generator
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must be seeded when <code>EVP_SealInit()</code> is called.
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If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
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external circumstances (see <em>RAND(7)</em>), the operation will fail.</p>
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<p>The public key must be RSA because it is the only OpenSSL public key
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algorithm that supports key transport.</p>
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<p>Envelope encryption is the usual method of using public key encryption
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on large amounts of data, this is because public key encryption is slow
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but symmetric encryption is fast. So symmetric encryption is used for
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bulk encryption and the small random symmetric key used is transferred
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using public key encryption.</p>
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<p>It is possible to call <code>EVP_SealInit()</code> twice in the same way as
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<code>EVP_EncryptInit()</code>. The first call should have <strong>npubk</strong> set to 0
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and (after setting any cipher parameters) it should be called again
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with <strong>type</strong> set to NULL.</p>
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<p>
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</p>
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<hr />
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<h1><a name="see_also">SEE ALSO</a></h1>
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<p><em>evp(7)</em>, <em>RAND_bytes(3)</em>,
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<em>EVP_EncryptInit(3)</em>,
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<em>EVP_OpenInit(3)</em>,
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<em>RAND(7)</em></p>
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<p>
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</p>
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<hr />
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<h1><a name="copyright">COPYRIGHT</a></h1>
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2020-03-02 12:19:21 -05:00
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<p>Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.</p>
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<p>Licensed under the OpenSSL license (the "License"). You may not use
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2020-03-02 11:50:34 -05:00
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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<a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>
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