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Fixed HMAC size for encryption

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Fabian Sauter 2021-12-27 12:09:33 +01:00 committed by GitHub
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commit 70d0ddf18a
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xep-0384.xml
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@ -330,7 +330,7 @@
<ol>
<li>Use HKDF-SHA-256 to generate 80 bytes of output from the message key by providing mk as HKDF input, 256 zero-bits as HKDF salt and &quot;OMEMO Message Key Material&quot; as HKDF info.</li>
<li>Divide the HKDF output into a 32-byte encryption key, a 32-byte authentication key and a 16 byte IV.</li>
<li>Encrypt the plaintext (which consists of a 32 bytes key and a 32 bytes HMAC as specified in the section about <link url="#protocol-message_encryption">Message Encryption</link>) using AES-256-CBC with PKCS#7 padding, using the encryption key and IV derived in the previous step.</li>
<li>Encrypt the plaintext (which consists of a 32 bytes key and a 16 bytes HMAC as specified in the section about <link url="#protocol-message_encryption">Message Encryption</link>) using AES-256-CBC with PKCS#7 padding, using the encryption key and IV derived in the previous step.</li>
<li>Split the associated data as returned by <tt>CONCAT</tt> into the original ad and the <tt>OMEMOMessage.proto</tt> structure.</li>
<li>Add the ciphertext to the <tt>OMEMOMessage.proto</tt> structure.</li>
<li>Serialize the <tt>OMEMOMessage.proto</tt> structure into a parseable byte array. To avoid potential problems regarding non-uniqueness of the serialization, make sure to only serialize <em>once</em> and to use that exact byte sequence in the following steps.</li>