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<body class="article toc2 toc-left">
<div id="header">
<h1>Encoding for Robust Immutable Storage (ERIS)</h1>
<div class="details">
<span id="author" class="author">pukkamustard</span><br>
<span id="email" class="email"><a href="mailto:pukkamustard@posteo.net">pukkamustard@posteo.net</a></span><br>
<span id="revdate">0.2.0-draft</span>
</div>
<div id="toc" class="toc2">
<div id="toctitle">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#_introduction">1. Introduction</a>
<ul class="sectlevel2">
<li><a href="#_objectives">1.1. Objectives</a></li>
<li><a href="#_scope">1.2. Scope</a></li>
<li><a href="#_previous_work">1.3. Previous work</a></li>
<li><a href="#_terminology">1.4. Terminology</a></li>
</ul>
</li>
<li><a href="#_specification_of_eris">2. Specification of ERIS</a>
<ul class="sectlevel2">
<li><a href="#_cryptographic_primitives">2.1. Cryptographic Primitives</a></li>
<li><a href="#_block_size">2.2. Block Size</a></li>
<li><a href="#_convergence_secret">2.3. Convergence Secret</a></li>
<li><a href="#_encoding">2.4. Encoding</a></li>
<li><a href="#_decoding">2.5. Decoding</a></li>
<li><a href="#_binary_encoding_of_read_capability">2.6. Binary Encoding of Read Capability</a></li>
<li><a href="#_urn">2.7. URN</a></li>
</ul>
</li>
<li><a href="#_applications">3. Applications</a>
<ul class="sectlevel2">
<li><a href="#_storage_and_transport_layers">3.1. Storage and Transport Layers</a></li>
<li><a href="#_namespaces">3.2. Namespaces</a></li>
</ul>
</li>
<li><a href="#_test_vectors">4. Test Vectors</a>
<ul class="sectlevel2">
<li><a href="#_machine_readable">4.1. Machine Readable</a></li>
<li><a href="#_large_content">4.2. Large content</a></li>
</ul>
</li>
<li><a href="#_implementations">5. Implementations</a></li>
<li><a href="#_acknowledgments">6. Acknowledgments</a></li>
<li><a href="#_changelog">Changelog</a></li>
<li><a href="#_copyright">Copyright</a></li>
<li><a href="#_references">References</a>
<ul class="sectlevel2">
<li><a href="#_normative_references">Normative References</a></li>
<li><a href="#_informative_references">Informative References</a></li>
</ul>
</li>
</ul>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="quoteblock abstract">
<blockquote>
This document describes the Encoding for Robust Immutable Storage (ERIS). ERIS is an encoding of arbitrary content into a set of uniformly sized, encrypted and content-addressed blocks as well as a short identifier (a URN). The content can be reassembled from the encrypted blocks only with this identifier. The encoding is defined independent of any storage and transport layer or any specific application. We illustrate how ERIS can be used as a building block for robust and decentralized applications.
</blockquote>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_introduction"><a class="anchor" href="#_introduction"></a>1. Introduction</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Unavailability of content on computer networks is a major cause for reduced reliability of networked services <a href="#Polleres2020">[Polleres2020]</a>.</p>
</div>
<div class="paragraph">
<p>Availability can be increased by caching content on multiple peers. However most content on the Internet is identified by its location. Caching location-addressed content is complicated as the content receives a new location.</p>
</div>
<div class="paragraph">
<p>An alternative to identifying content by its location is to identify content by its content itself. This is called content-addressing. The hash of some content is computed and used as an unique identifier for the content.</p>
</div>
<div class="paragraph">
<p>Caching content-addressed content and making it available redundantly is much easier as the content is completely decoupled from any physical location. Integrity of content is automatically ensured with content-addressing (when using a cryptographic hash) as the identifier of the content can be computed to check that the content matches the requested identifier.</p>
</div>
<div class="paragraph">
<p>However, naive content-addressing has certain drawbacks:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Large content is stored as a large chunk of data. In order to optimize storage and network operations it is better to split up content into smaller uniformly sized blocks and reassemble blocks when needed.</p>
</li>
<li>
<p>Confidentiality: Content is readable by all peers involved in transporting, caching and storing content.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>ERIS addresses these issues by splitting content into small uniformly sized and encrypted blocks.</p>
</div>
<div class="paragraph">
<p>Encodings similar to ERIS are already widely-used in applications and protocols such as GNUNet (see <a href="#_previous_work">Section 1.3</a>), BitTorrent <a href="#BEP52">[BEP52]</a>, Freenet <a href="#Freenet">[Freenet]</a> and others. However, they all use slightly different encodings that are tied to the respective protocols and applications. ERIS defines an encoding independant of any specific protocol or application and decouples content from transport and storage layers. ERIS may be seen as a modest step towards Information-Centric Networking <a href="#RFC7927">[RFC7927]</a>.</p>
</div>
<div class="sect2">
<h3 id="_objectives"><a class="anchor" href="#_objectives"></a>1.1. Objectives</h3>
<div class="paragraph">
<p>The objectives of ERIS are:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">Availability </dt>
<dd>
<p>Content encoded with ERIS can be easily replicated and cached.</p>
</dd>
<dt class="hdlist1">Integrity </dt>
<dd>
<p>Integrity of content can be verified efficiently.</p>
</dd>
<dt class="hdlist1">URN reference </dt>
<dd>
<p>ERIS encoded content can be referrenced with a single URN.</p>
</dd>
<dt class="hdlist1">Storage efficiency </dt>
<dd>
<p>ERIS can be used to encode small content (&lt; 1 kibibyte) as well as large content (&gt; many gibibyte) with reasonable storage overhead.</p>
</dd>
<dt class="hdlist1">Simplicity </dt>
<dd>
<p>The encoding should be as simple as possible in order to allow correct implementation on various platforms and in various languages.</p>
</dd>
</dl>
</div>
</div>
<div class="sect2">
<h3 id="_scope"><a class="anchor" href="#_scope"></a>1.2. Scope</h3>
<div class="paragraph">
<p>ERIS describes how arbitrary content (sequence of bytes) can be encoded into a set of uniformly sized blocks and an identifier with which the content can be decoded from the set of blocks.</p>
</div>
<div class="paragraph">
<p>ERIS does not prescribe how the blocks should be stored or transported over network. The only requirement is that a block can be referenced and accessed (if available) by the hash value of the contents of the block. In section <a href="#_storage_and_transport_layers">Section 3.1</a> we show how existing technology (including IPFS) can be used to store and transport blocks.</p>
</div>
<div class="paragraph">
<p>There is also no support for grouping content or mutating content. In section <a href="#_namespaces">Section 3.2</a> we describe how such functionality can be implemented on top of ERIS.</p>
</div>
<div class="paragraph">
<p>The lack of certain functionalities is intentional. ERIS is an attempt to find a minimal common basis on which higher functionality can be built. Lacking functionality in ERIS is an acknowledgment that there are many ways of implementing such functionality at a different layer that may be optimized for certain use-cases.</p>
</div>
</div>
<div class="sect2">
<h3 id="_previous_work"><a class="anchor" href="#_previous_work"></a>1.3. Previous work</h3>
<div class="paragraph">
<p>ERIS is inspired and based on the encoding used in the file-sharing application of <a href="https://gnunet.org/">GNUNet</a> - Encoding for Censorship-Resistant Sharing (ECRS) <a href="#ECRS">[ECRS]</a>.</p>
</div>
<div class="paragraph">
<p>ERIS differs from ECRS in following points:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">Cryptographic primitives </dt>
<dd>
<p>ECRS itself does not specify any cryptographic primitives but the GNUNet implementation uses the SHA-512 hash and AES cipher. ERIS uses the Blake2b-256 cryptographic hash <a href="#RFC7693">[RFC7693]</a> and the ChaCha20 stream cipher <a href="#RFC8439">[RFC8439]</a>. This improves performance, storage efficiency (as hash references are smaller) and allows a convergence secret to be used (via Blake2b keyed hashing; see <a href="#_convergence_secret">Section 2.3</a>).</p>
</dd>
<dt class="hdlist1">Block size </dt>
<dd>
<p>ECRS uses a fixed block size of 32 KiB. This can be very inefficient when encoding many small pieces of content. ERIS allows a block size of 1 KiB or 32 KiB, allowing efficient encoding of small and large content (see <a href="#_block_size">Section 2.2</a>).</p>
</dd>
<dt class="hdlist1">URN </dt>
<dd>
<p>ECRS does not specify an URN for referring to encoded content (this is specified as part of the GNUNet file-sharing application). ERIS specifies an URN for encoded content regardless of encoding application or storage and transport layer (see <a href="#_urn">Section 2.7</a>).</p>
</dd>
<dt class="hdlist1">Namespaces </dt>
<dd>
<p>ECRS defines two mechanisms for grouping and discovering encoded content (SBlock and KBlock). ERIS does not specify any such mechanisms (see <a href="#_namespaces">Section 3.2</a>).</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>Other related projects include Tahoe-LAFS and Freenet. The reader is referred to the ECRS paper <a href="#ECRS">[ECRS]</a> for an in-depth explanation and comparison of related projects.</p>
</div>
<div class="paragraph">
<p>ERIS is being developed in close collaboration with the <a href="https://datashards.net/">Datashards</a> initiative.</p>
</div>
</div>
<div class="sect2">
<h3 id="_terminology"><a class="anchor" href="#_terminology"></a>1.4. Terminology</h3>
<div class="paragraph">
<p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 <a href="#RFC2119">[RFC2119]</a>.</p>
</div>
<div class="paragraph">
<p>We use binary prefixes for multiples of bytes, i.e: 1024 bytes is 1 kibibyte (KiB), 1024 kibibytes is 1 mebibyte (MiB) and 1024 mebibytes is 1 gigibytes (GiB).</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_specification_of_eris"><a class="anchor" href="#_specification_of_eris"></a>2. Specification of ERIS</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_cryptographic_primitives"><a class="anchor" href="#_cryptographic_primitives"></a>2.1. Cryptographic Primitives</h3>
<div class="paragraph">
<p>The cryptographic primitives used by ERIS are a cryptographic hash funciton, a symmetric key cipher and a padding algorithm. The hash function and cipher are readily available in open-source libraries such as <a href="https://github.com/jedisct1/libsodium">libsodium</a> or <a href="https://monocypher.org/">Monocypher</a>. The padding algorithm can be implemented with reasonable effort.</p>
</div>
<div class="sect3">
<h4 id="_cryptographic_hash_function"><a class="anchor" href="#_cryptographic_hash_function"></a>2.1.1. Cryptographic Hash Function</h4>
<div class="paragraph">
<p>Blake2b <a href="#RFC7693">[RFC7693]</a> with output size of 256 bit (32 byte). We use the keying feature and refer to the key used for keying Blake2b as the <em>hashing key</em>.</p>
</div>
<div class="paragraph">
<p>Provides the functions <code>Blake2b-256(INPUT, HASHING-KEY)</code> for keyed hashing and <code>Blake2b-256(INPUT)</code> for unkeyed hashing.</p>
</div>
</div>
<div class="sect3">
<h4 id="_symmetric_key_cipher"><a class="anchor" href="#_symmetric_key_cipher"></a>2.1.2. Symmetric Key Cipher</h4>
<div class="paragraph">
<p>ChaCha20 (IETF variant) <a href="#RFC8439">[RFC8439]</a>. Provides <code>ChaCha20(INPUT, KEY)</code>,  where <code>INPUT</code> is an arbirtarty length byte sequence and <code>KEY</code> is the 256 bit encryption key. The output is the encrypted byte sequence.</p>
</div>
<div class="paragraph">
<p>The 32 bit initial counter as well as the 96 bit nonce are set to 0. We can safely use the zero nonce as we never reuse a key.</p>
</div>
<div class="paragraph">
<p>Decryption is done with the same function where <code>INPUT</code> is the encrypted byte sequence.</p>
</div>
</div>
<div class="sect3">
<h4 id="_padding_algorithm"><a class="anchor" href="#_padding_algorithm"></a>2.1.3. Padding Algorithm</h4>
<div class="paragraph">
<p>We use a byte padding scheme to ensure that input content size is a multiple of a block size. Provides following functions:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>PAD(INPUT,BLOCK-SIZE)</code> </dt>
<dd>
<p>For <code>INPUT</code> of size <code>n</code> adds a mandatory byte valued <code>0x80</code> (hexadecimal) to <code>INPUT</code> followed by <code>m &lt; BLOCK-SIZE - 1</code> bytes valued <code>0x00</code> such that <code>n + m + 1</code> is a multiple of <code>BLOCK-SIZE</code>.</p>
</dd>
<dt class="hdlist1"><code>UNPAD(INPUT,BLOCK-SIZE)</code> </dt>
<dd>
<p>Starts reading bytes from the end of <code>INPUT</code> until a <code>0x80</code> is read and then returns bytes of <code>INPUT</code> before the <code>0x80</code>. Throws an error if a value other than <code>0x00</code> is read before reading <code>0x80</code> or if no <code>0x80</code> is read after reading  <code>BLOCK-SIZE - 1</code> bytes from the end.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>This is the padding algorithm implemented in <a href="https://libsodium.gitbook.io/doc/padding">libsodium</a><sup class="footnote">[<a id="_footnoteref_1" class="footnote" href="#_footnotedef_1" title="View footnote.">1</a>]</sup>.</p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_block_size"><a class="anchor" href="#_block_size"></a>2.2. Block Size</h3>
<div class="paragraph">
<p>ERIS uses two block sizes: 1KiB (1024 bytes) and 32KiB (32768 bytes). The block size must be specified when encoding content.</p>
</div>
<div class="paragraph">
<p>Both block sizes can be used to encode content of arbitrary size. The block size of 1KiB is an optimization towards smaller content.</p>
</div>
<div class="paragraph">
<p>Content smaller than TODO SHOULD be encoded with block size 1KiB, content larger than TODO SHOULD be encoded with block size 32KiB.</p>
</div>
<div class="paragraph">
<p>The block size is encoded in the read capability and the decoding process is capable of handling both cases.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph">
<p>When using block size 32KiB to encode content smaller than 1KiB, the content will be encoded in a 32KiB block. This is a storage overhead of over 3100%. When encoding very many pieces of small content (e.g. short messages or cartographic nodes) this overhead is not acceptable.</p>
</div>
<div class="paragraph">
<p>On the other hand, using small block sizes increases the number of internal nodes that must be used to encode the content (see <a href="#_collect_reference_key_pairs_in_nodes">Section 2.4.3</a>). When encoding larger content it is more efficient to use a block size of 32KiB.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="_convergence_secret"><a class="anchor" href="#_convergence_secret"></a>2.3. Convergence Secret</h3>
<div class="paragraph">
<p>Using the hash of the content as key is called <em>convergent encryption</em>.</p>
</div>
<div class="paragraph">
<p>Because the hash of the content is deterministically computed from the content, the key will be the same when the same content is encoded twice. This results in de-duplication of content. Convergent encryption suffers from two known attacks: The Confirmation Of A File Attack and The Learn-The-Remaining-Information Attack <a href="#Zooko2008">[Zooko2008]</a>. A defense against both attacks is to use a <em>convergence secret</em>. This results in different encoding of the same content with different convergence secret.</p>
</div>
<div class="paragraph">
<p>If no convergence secret is specified a null convergence secret MUST be used (32 bytes of zeroes).</p>
</div>
<div class="paragraph">
<p>The convergence secret is implemented as the keying feature of the Blake2 cryptographic hash <a href="#RFC7693">[RFC7693]</a>.</p>
</div>
</div>
<div class="sect2">
<h3 id="_encoding"><a class="anchor" href="#_encoding"></a>2.4. Encoding</h3>
<div class="paragraph">
<p>Inputs to the encoding process are:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>CONTENT</code> </dt>
<dd>
<p>An arbitary length byte sequence of content to be encoded.</p>
</dd>
<dt class="hdlist1"><code>CONVERGENCE-SECRET</code> </dt>
<dd>
<p>A 256 bit (32 byte) byte sequence (see <a href="#_convergence_secret">Section 2.3</a>).</p>
</dd>
<dt class="hdlist1"><code>BLOCK-SIZE</code> </dt>
<dd>
<p>The block size used for encoding in bytes can be either 1024 (1KiB) or 32768 (32KiB) (see <a href="#_block_size">Section 2.2</a>).</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>Content is encoded by first splitting into uniformly sized blocks, encrypting the blocks and computing references to the blocks. If there are multiple references to blocks they are collected in nodes that have the same size as content blocks. The nodes are encrypted and references to the nodes are computed. This process is repeated until there is a single root reference.</p>
</div>
<div class="paragraph">
<p>References to nodes and blocks of content consist of a reference to an encrypted block and a key to decrypt the block - a <em>reference-key pair</em>. The process of encrypting a block and computing a reference-key pair is explained in <a href="#_encrypt_block_and_compute_reference_key_pair">Section 2.4.2</a>.</p>
</div>
<div class="paragraph">
<p>The encoding process constructs a tree of reference-key pairs that reference nodes that hold references to nodes of a lower level or to content.</p>
</div>
<div class="paragraph">
<p>The number of reference-key pairs collected into a node is called the <em>arity</em> of the tree and depends on the block size. For block size 1KiB the arity of the tree is 16, for block size 32KiB the arity is 512.</p>
</div>
<div class="paragraph">
<p>An encoding of a content that is split into eight blocks is depicted in <a href="#figure_merkle_tree">Figure 1</a>. For illustration purposes the tree is of arity 2 (instead of 16 or 512).</p>
</div>
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<div class="title">Figure 1. Encoding of content as tree. Solid edges are concatenations of reference-key pairs as described in <a href="#_collect_reference_key_pairs_in_nodes">Section 2.4.3</a>. Dotted edges are encryption and computation of reference-key pairs as described in <a href="#_encrypt_block_and_compute_reference_key_pair">Section 2.4.2</a>.</div>
</div>
<div class="paragraph">
<p>The block size, the level of the root reference and the root reference-key pair itself are the necessary pieces of information required to decode content. The tuple consisting of block size, level, root reference and key is called the <em>read capability</em>.</p>
</div>
<div class="paragraph">
<p>The encrypted blocks and the read capability are the outputs of the encoding process.</p>
</div>
<div class="paragraph">
<p>A pseudo-code implementation of the encoding process is provided in the following. Note that the pseudo-code implementation is naive and given for illustration purposes only. It is RECOMMENDED that imlementations use a streaming encoding process (as described in <a href="#_streaming">Section 2.4.4</a>) which allows encoding of content larger than the available memory.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-pseudocode" data-lang="pseudocode">ERIS-Encode(CONTENT, CONVERGENCE-SECRET, BLOCK-SIZE):
    // initialize empty list of blocks to be output
    BLOCKS := []

    // initialize level to 0
    LEVEL := 0

    // split the input content into uniformly sized blocks and encode
    LEVEL-0-BLOCKS, RK-PAIRS := Split-Content(CONTENT, BLOCK-SIZE)

    // add blocks from level 0 to blocks to be output
    BLOCKS := BLOCKS ++ LEVEL-0-BLOCKS

    // loop until there is a single root reference
    WHILE Length(RK-PAIRS) &gt; 1:
        LEVEL-BLOCKS, RK-Pairs := Collect-RK-Pairs(RK-PAIRS, CONVERGENCE-SECRET, BLOCK-SIZE)

        // add blocks to blocks to be output and increase the level counter
        BLOCKS := BLOCKS ++ LEVEL-BLOCKS
        LEVEL := LEVEL + 1

    // extract the root reference-key pair
    ROOT-RK-PAIR := RK-PAIRS[0]
    ROOT-REFERENCE, ROOT-KEY := ROOT-RK-PAIR

    // return blocks and read-capability
    RETURN BLOCKS, BLOCK-SIZE, LEVEL, ROOT-REFERENCE, ROOT-KEY</code></pre>
</div>
</div>
<div class="paragraph">
<p>The sub-process <code>Split-Content</code> and <code>Collect-RK-Pairs</code> are explained in the following sections.</p>
</div>
<div class="sect3">
<h4 id="_splitting_input_content_into_blocks"><a class="anchor" href="#_splitting_input_content_into_blocks"></a>2.4.1. Splitting Input Content into Blocks</h4>
<div class="paragraph">
<p>Input content is split into blocks of size at most block size such that only the last content block may be smaller than block size.</p>
</div>
<div class="paragraph">
<p>The last content block is always padded according to the padding algorithm to block size. If the size of the padded last block is larger than block size it is split into content blocks of block size.</p>
</div>
<div class="paragraph">
<p>A pseudo code implementation:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-pseudocode" data-lang="pseudocode">Split-Content(CONTENT,CONVERGENCE-SECRET,BLOCK-SIZE):
    // initialize list of blocks and reference-key pairs to output
    BLOCKS := []
    RK-PAIRS := []

    // read blocks of size BLOCK-SIZE from CONTENT
    WHILE CONTENT-BLOCK, LAST? := READ(CONTENT, BLOCK-SIZE):

        IF LAST?:
            // pad block if it is the last
            PADDED := PAD(CONTENT-BLOCK, BLOCK-SIZE)

            IF Length(PADDED) &gt; BLOCK-SIZE:
                PADDED-0, PADDED-1 := SPLIT(PADDED, BLOCK-SIZE)
                ENCRYPTED-BLOCK-0, RK-PAIR-0 := Encrypt-Block(PADDED-0, CONVERGENCE-SECRET)
                ENCRYPTED-BLOCK-1, RK-PAIR-1 := Encrypt-Block(PADDED-1, CONVERGENCE-SECRET)
                BLOCKS := BLOCKS ++ [ENCRYPTED-BLOCK-0, ENCRYPTED-BLOCK-1]
                RK-PAIRS := RK-PAIRS ++ [RK-PAIR-0, RK-PAIR-1]
            ELSE:
                ENCRYPTED-BLOCK, RK-PAIR := Encrypt-Block(PADDED, CONVERGENCE-SECRET)
                BLOCKS := BLOCKS ++ [ENCRYPTED-BLOCK]
                RK-PAIRS := RK-PAIRS ++ [RK-PAIR]

         ELSE:
            ENCRYPTED-BLOCK, RK-PAIR := Encrypt-Block(CONTENT-BLOCK, CONVERGENCE-SECRET)
            BLOCKS := BLOCKS ++ [ENCRYPTED-BLOCK]
            RK-PAIRS := RK-PAIRS ++ [RK-PAIR]

    RETURN BLOCKS, RK-PAIRS</code></pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
If the length of the last content block is exactly block size, then padding will result in a padded block that is double the block size and must be split.
</td>
</tr>
</table>
</div>
</div>
<div class="sect3">
<h4 id="_encrypt_block_and_compute_reference_key_pair"><a class="anchor" href="#_encrypt_block_and_compute_reference_key_pair"></a>2.4.2. Encrypt Block and Compute Reference-Key Pair</h4>
<div class="paragraph">
<p>A <em>reference-key pair</em> is a pair consisting of a reference to an encrypted block and the key to decrypt the block. Reference and key are both 32 bytes long. The concatenation of  a reference-key pair is 64 bytes long (512 bits).</p>
</div>
<div class="paragraph">
<p>The <code>Encrypt-Block</code> function encrypts a block and returns the encrypted block along with the reference-key pair:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-pseudocode" data-lang="pseudocode">Encrypt-Block(INPUT, CONVERGENCE-SECRET):
    KEY := Blake2b-256(INPUT,CONVERGENCE-SECRET)
    ENCRYPTED-BLOCK := ChaCha20(INPUT,KEY)
    REFERENCE := Blake2b-256(ENCRYPTED-BLOCK)
    RETURN ENCRYPTED-BLOCK, REFERENCE, KEY</code></pre>
</div>
</div>
<div class="paragraph">
<p>The convergence-secret MUST NOT be used to compute the reference to the encrypted block.</p>
</div>
</div>
<div class="sect3">
<h4 id="_collect_reference_key_pairs_in_nodes"><a class="anchor" href="#_collect_reference_key_pairs_in_nodes"></a>2.4.3. Collect Reference-Key Pairs in Nodes</h4>
<div class="paragraph">
<p>Reference-key pairs are collected into nodes of size block size by concatenating reference-key pair. The node is encrypted, and a reference-key pair to the node is computed. This results in a sequence of reference-key pairs that refer to nodes containing reference-key pairs at a lower level - a tree.</p>
</div>
<div class="paragraph">
<p>If there are less than arity number of references-key pairs to collect in a node, then the node is filled with missing number of <em>null reference-key pairs</em> - 64 bytes of zeros. The size of a node is always equal the block size (implemented with the <code>FILL-WITH-NULL-RK-PAIRS</code> function).</p>
</div>
<div class="paragraph">
<p>A pseudo-code implementation of <code>Collect-RK-Pairs</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-pseudocode" data-lang="pseudocode">Collect-RK-Pairs(INPUT-RK-PAIRS, CONVERGENCE-SECRET, BLOCK-SIZE):
    // number of reference-key pairs in a node
    ARITY := BLOCK-SIZE / 64

    // initialize blocks and reference-key pairs to output
    BLOCKS := []
    OUTPUT-RK-PAIRS := []

    // take ARITY reference-key pairs from INPUT-RK-PAIRS at a time
    WHILE RK-PAIRS-FOR-NODE := TAKE(INPUT-RK-PAIRS, ARITY):
        // make sure there are exactly ARITY reference-key pairs in node
        RK-PAIRS-FOR-NODE := FILL-WITH-NULL-RK-PAIRS(RK-PAIRS-FOR-NODE, ARITY)

        // concat reference-key pairs to node
        NODE := CONCAT(RK-PAIRS-FOR-NODE)

        // encrypt node and compute reference-key pair
        BLOCK, RK-TO-NODE := Encrypt-Block(NODE, CONVERGENCE-SECRET)

        // add node to output
        BLOCKS := BLOCKS ++ [BLOCK]
        OUTPUT-RK-PAIRS := OUTPUT-RK-PAIRS ++ [RK-TO-NODE]

    RETURN BLOCKS, OUTPUT-RK-PAIRS</code></pre>
</div>
</div>
</div>
<div class="sect3">
<h4 id="_streaming"><a class="anchor" href="#_streaming"></a>2.4.4. Streaming</h4>
<div class="paragraph">
<p>The encoding process can be implemented to encode a stream of content while immediately outputting encrypted blocks when ready and eagerly collecting reference-key pairs to nodes. This allows the encoding of larger-than-memory content.</p>
</div>
<div class="paragraph">
<p>For an example, see <a href="https://gitlab.com/openengiadina/eris/-/raw/main/eris/encode.scm">the reference Guile implementation</a>.</p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_decoding"><a class="anchor" href="#_decoding"></a>2.5. Decoding</h3>
<div class="paragraph">
<p>Given an ERIS read capability and access to blocks via a block-storage the content can be decoded.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-pseudocode" data-lang="pseudocode">ERIS-Decode-Recurse(LEVEL, REFERENCE, KEY):
    IF LEVEL == 0:
        ENCRYPTED-CONTENT-BLOCK := Block-Storage-Get(REFERENCE)
        RETURN ChaCha20(CONTENT-BLOCK, KEY)
    ELSE:
        ENCRYPTED-NODE := Block-Storage-Get(REFERENCE)
        NODE := ChaCha20(ENCRYPTED, KEY)
        OUTPUT := []
        WHILE SUB-REFERENCE, SUB-KEY := Read-RK-Pair-From-Node(NODE):
            OUTPUT := OUTPUT ++ [ERIS-DECODE-Recurse(LEVEL - 1, SUB-REFERENCE, SUB-KEY)]
        RETURN CONCAT(OUTPUT)

ERIS-Decode(BLOCK-SIZE, LEVEL, ROOT-REFERENCE, ROOT-KEY):
    PADDED := ERIS-Decode-Recurse(LEVEL, ROOT-REFERENCE, ROOT-KEY)
    RETURN UNPAD(PADDED, BLOCK-SIZE)</code></pre>
</div>
</div>
<div class="paragraph">
<p>Where the block-storage can be accessed as follows:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>Block-Storage-Get(REFERENCE)</code> </dt>
<dd>
<p>Returns a block such that <code>Blake2b-256(Block-Storage-Get(REFERENCE)) == REFERENCE</code> or throws an error.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>A streaming decoding procedure can be implemented where the content can be output block wise and does not need to be kept in memory for unpadding. For an example, see <a href="https://gitlab.com/openengiadina/eris/-/raw/main/eris/decode.scm">the reference Guile implementation</a>.</p>
</div>
<div class="sect3">
<h4 id="_random_access"><a class="anchor" href="#_random_access"></a>2.5.1. Random Access</h4>
<div class="paragraph">
<p>A decoder that allows random access to the encoded content can be implemented by decoding selected sub-trees.</p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_binary_encoding_of_read_capability"><a class="anchor" href="#_binary_encoding_of_read_capability"></a>2.6. Binary Encoding of Read Capability</h3>
<div class="paragraph">
<p>The read-capability consisting of the block-size, level of root reference-key pair as well as the root reference-key pair form the necessary pieces of information required to decode content.</p>
</div>
<div class="paragraph">
<p>We specify an binary encoding of the read-capability 66 bytes:</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 33.3333%;">
<col style="width: 33.3333%;">
<col style="width: 33.3334%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Byte offset</th>
<th class="tableblock halign-left valign-top">Content</th>
<th class="tableblock halign-left valign-top">Length (in bytes)</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">0</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">block size (<code>0x00</code> for block size 1KiB and <code>0x01</code> for block size 32KiB)</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">1</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">1</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">level of root reference-key pair as unsigned integer</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">1</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">2</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">root reference</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">32</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">34</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">root key</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">32</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>The initial field (block size) also encodes the ERIS version. Future versions of ERIS MUST use different codes to encode block sizes.</p>
</div>
<div class="paragraph">
<p>Note that using a single byte to encode the level limits the size of content that can be encoded with ERIS. However, the size of the largest encodable content is approximately 1e300 TiB, which seems to be sufficient for any conceivable practical applications (including an index of all atoms in the universe).</p>
</div>
</div>
<div class="sect2">
<h3 id="_urn"><a class="anchor" href="#_urn"></a>2.7. URN</h3>
<div class="paragraph">
<p>A read-capability can be encoded as an URN: <code>urn:eris:BASE32-READ-CAPABILITY</code>, where <code>BASE32-READ-CAPABILITY</code> is the unpadded Base32 <a href="#RFC4648">[RFC4648]</a> encoding of the read capability.</p>
</div>
<div class="paragraph">
<p>For example the ERIS URN of the UTF-8 encoded string "Hello world!" (with block size 1KiB and null convergence secret):</p>
</div>
<div class="paragraph">
<p><code>urn:erisx2:AAAD77QDJMFAKZYH2DXBUZYAP3MXZ3DJZVFYQ5DFWC6T65WSFCU5S2IT4YZGJ7AC4SYQMP2DM2ANS2ZTCP3DJJIRV733CRAAHOSWIYZM3M</code></p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_applications"><a class="anchor" href="#_applications"></a>3. Applications</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_storage_and_transport_layers"><a class="anchor" href="#_storage_and_transport_layers"></a>3.1. Storage and Transport Layers</h3>

</div>
<div class="sect2">
<h3 id="_namespaces"><a class="anchor" href="#_namespaces"></a>3.2. Namespaces</h3>

</div>
</div>
</div>
<div class="sect1">
<h2 id="_test_vectors"><a class="anchor" href="#_test_vectors"></a>4. Test Vectors</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_machine_readable"><a class="anchor" href="#_machine_readable"></a>4.1. Machine Readable</h3>
<div class="paragraph">
<p>A set of test vectors are provided in the  <a href="https://gitlab.com/openengiadina/eris/-/tree/main/test-vectors">ERIS repository</a>. Implementations of the ERIS encoding MUST be able to satisfy the test vectors.</p>
</div>
<div class="paragraph">
<p>The test vectors are given as machine-readable JSON files. For example the test vector <code>eris-test-vector-00.json</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-json" data-lang="json">{
  "id": 0,
  "name": "short string (block size 1KiB)",
  "description": "Encode the UTF-8 encoding of the string \"Hello world!\" with block-size 1KiB and null convergence-secret.",
  "content": "JBSWY3DPEB3W64TMMQQQ",
  "convergence-secret": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
  "block-size": 1024,
  "read-capability": {
    "block-size": 1024,
    "level": 0,
    "root-reference": "H77AGSYKAVTQPUHODJTQA7WZPTWGTTKLRB2GLMF5H53NEKFJ3FUQ",
    "root-key": "CPTDEZH4ALSLCBR7INTIBWLLGMJ7MNFFCGX7PMKEAA52KZDDFTNQ"
  },
  "urn": "urn:erisx2:AAAD77QDJMFAKZYH2DXBUZYAP3MXZ3DJZVFYQ5DFWC6T65WSFCU5S2IT4YZGJ7AC4SYQMP2DM2ANS2ZTCP3DJJIRV733CRAAHOSWIYZM3M",
  "blocks": {
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
  }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>The fields of JSON test vectors are:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>id</code> </dt>
<dd>
<p>Numeric identifier of the test vector.</p>
</dd>
<dt class="hdlist1"><code>name</code> </dt>
<dd>
<p>Short human readable name.</p>
</dd>
<dt class="hdlist1"><code>description</code> </dt>
<dd>
<p>Human readable description of the test.</p>
</dd>
<dt class="hdlist1"><code>content</code> </dt>
<dd>
<p>The binary content to be encoded as Base32 (unpadded) string.</p>
</dd>
<dt class="hdlist1"><code>convergence-secret</code> </dt>
<dd>
<p>The convergence secret to be used as Base32 string.</p>
</dd>
<dt class="hdlist1"><code>block-size</code> </dt>
<dd>
<p>Block size that should be used for encoding in bytes (either 1024 or 32768).</p>
</dd>
<dt class="hdlist1"><code>read-capability</code> </dt>
<dd>
<p>JSON map containing the components of the read capability. This is not used in tests but is here as a help for developers.</p>
</dd>
<dt class="hdlist1"><code>urn</code> </dt>
<dd>
<p>The ERIS URN of the content.</p>
</dd>
<dt class="hdlist1"><code>blocks</code> </dt>
<dd>
<p>A JSON map of blocks required to decode the content given the URN. Key and field are encoded as Base32 strings.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>Implementations MUST verify that the content encodes to the URN given the specified block size and convergence secret and verify that given the URN and blocks the content can be decoded.</p>
</div>
</div>
<div class="sect2">
<h3 id="_large_content"><a class="anchor" href="#_large_content"></a>4.2. Large content</h3>
<div class="paragraph">
<p>In order to verify implementations that encode content by streaming (see <a href="#_streaming">Section 2.4.4</a>) URNs of large contents that are generated in a specified way are provided:</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
</colgroup>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Test name</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Content size</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Block size</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">URN</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Level of root reference</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">100MiB (block size 1KiB)</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">100MiB</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">1KiB</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>urn:erisx2:AACXPZNDNXFLO4IOMF6VIV2ZETGUJEUU7GN4AHPWNKEN6KJMCNP6YNUMVW2SCGZUJ4L3FHIXVECRZQ3QSBOTYPGXHN2WRBMB27NXDTAP24</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">5</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">1GiB (block size 32KiB)</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">1GiB</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">32KiB</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>urn:erisx2:AEBFG37LU5BM5N3LXNPNMGAOQPZ5QTJAV22XEMX3EMSAMTP7EWOSD2I7AGEEQCTEKDQX7WCKGM6KQ5ALY5XJC4LMOYQPB2ZAFTBNDB6FAA</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">2</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">256GiB (block size 32KiB)</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">256GiB</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">32KiB</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>urn:erisx2:AEBZHI55XJYINGLXWKJKZHBIXN6RSNDU233CY3ELFSTQNSVITBSVXGVGBKBCS4P4M5VSAUOZSMVAEC2VDFQTI5SEYVX4DN53FTJENWX4KU</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">3</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>Content is the ChaCha20 stream using a null nonce and the key which is the Blake2b hash of the UTF-8 encoded test name (e.g. <code>KEY := Blake2b-256("100MiB (block size 1KiB)")</code>). The ChaCha20 stream can be computed by encoding a null byte sequence (e.g. <code>CHACHA20_STREAM := ChaCha20(NULL, KEY)</code>).</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_implementations"><a class="anchor" href="#_implementations"></a>5. Implementations</h2>
<div class="sectionbody">
<div class="paragraph">
<p>A list of known implementations that satisify the test vectors:</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Name</th>
<th class="tableblock halign-left valign-top">Programming language</th>
<th class="tableblock halign-left valign-top">License</th>
<th class="tableblock halign-left valign-top">Notes</th>
<th class="tableblock halign-left valign-top">Homepage</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>guile-eris</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Guile</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">GPL-3.0-or-later</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Reference implementation</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://gitlab.com/openengiadina/eris/" class="bare">https://gitlab.com/openengiadina/eris/</a></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>elixir-eris</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Elixir</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">GPL-3.0-or-later</p></td>
<td class="tableblock halign-left valign-top"></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://gitlab.com/openengiadina/elixir-eris/" class="bare">https://gitlab.com/openengiadina/elixir-eris/</a></p></td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="sect1">
<h2 id="_acknowledgments"><a class="anchor" href="#_acknowledgments"></a>6. Acknowledgments</h2>
<div class="sectionbody">

</div>
</div>
<div class="sect1">
<h2 id="_changelog"><a class="anchor" href="#_changelog"></a>Changelog</h2>
<div class="sectionbody">
<h3 id="_v0_1_0_11_june_2020" class="discrete"><a href="eris-v0.1.html">v0.1.0 (11. June 2020)</a></h3>
<div class="paragraph">
<p>Initial version.</p>
</div>
<h3 id="_v0_2_0_draft_unreleased" class="discrete"><a href="http://purl.org/eris">v0.2.0-draft (UNRELEASED)</a></h3>
<div class="paragraph">
<p>Major update of encoding that removes the <em>verification capability</em> - ability to verify integrity of content without reading content.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_copyright"><a class="anchor" href="#_copyright"></a>Copyright</h2>
<div class="sectionbody">
<div class="paragraph">
<p>This work is licensed under a <a href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_references"><a class="anchor" href="#_references"></a>References</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_normative_references"><a class="anchor" href="#_normative_references"></a>Normative References</h3>
<div class="ulist bibliography">
<ul class="bibliography">
<li>
<p><a id="RFC2119"></a>[RFC2119] S. Bradner, <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>, 1997.</p>
</li>
<li>
<p><a id="RFC4648"></a>[RFC4648] S. Josefsson, <a href="https://tools.ietf.org/html/rfc4648">The Base16, Base32, and Base64 Data Encodings</a>, 2006.</p>
</li>
<li>
<p><a id="RFC7693"></a>[RFC7693] M-J. Saarinen and J-P. Aumasson, <a href="https://tools.ietf.org/html/rfc7693">The BLAKE2 Cryptographic Hash and Message Authentication Code (MAC)</a>, 2015.</p>
</li>
<li>
<p><a id="RFC8439"></a>[RFC8439] Nir and Langley, <a href="https://tools.ietf.org/html/rfc8439">ChaCha20 and Poly1305 for IETF Protocols</a>, 2018.</p>
</li>
<li>
<p><a id="RFC8141"></a>[RFC8141] Saint-Andre, Filament and Klensin, <a href="https://tools.ietf.org/html/rfc8141">Uniform Resource Names (URNs)</a>, 2017.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="_informative_references"><a class="anchor" href="#_informative_references"></a>Informative References</h3>
<div class="ulist bibliography">
<ul class="bibliography">
<li>
<p><a id="BEP52"></a>[BEP52]  <a href="http://bittorrent.org/beps/bep_0052.html">The BitTorrent Protocol Specification v2</a>, 2017.</p>
</li>
<li>
<p><a id="ECRS"></a>[ECRS] Grothoff, et al., <a href="https://grothoff.org/christian/ecrs.pdf">An encoding for censorship-resistant sharing</a>, 2003.</p>
</li>
<li>
<p><a id="Freenet"></a>[Freenet] Clarke, et al., <a href="http://bourbon.usc.edu/cs694-s09/papers/freenet.pdf">Freenet: A distributed anonymous information storage and retrieval system</a>, 2001.</p>
</li>
<li>
<p><a id="Polleres2020"></a>[Polleres2020] Polleres, et al., <a href="https://epub.wu.ac.at/6371/1/IPM_workingpaper_02_2018.pdf">A more decentralized vision for Linked Data</a>, 2020.</p>
</li>
<li>
<p><a id="RFC7927"></a>[RFC7927] Kutscher et. al. <a href="https://tools.ietf.org/html/rfc7927">Information-Centric Networking (ICN) Research Challenges</a>, 2016.</p>
</li>
<li>
<p><a id="Zooko2008"></a>[Zooko2008] Zooko Wilcox-O&#8217;Hearn. <a href="https://tahoe-lafs.org/hacktahoelafs/drew_perttula.html">Drew Perttula and Attacks on Convergent Encryption</a>, 2008.</p>
</li>
<li>
<p><a id="content-addressable-rdf"></a>[content-addressable-rdf] openEngiadina. <a href="https://openengiadina.net/papers/content-addressable-rdf.html">Content-addressable RDF</a>, 2020.</p>
</li>
<li>
<p><a id="rdf-signify"></a>[rdf-signify] openEngiadina. <a href="https://openengiadina.net/papers/rdf-signify.html">RDF Signify</a>, 2020.</p>
</li>
<li>
<p><a id="RFC7049"></a>[RFC7049] C. Bormann &amp; P. Hoffman. <a href="https://tools.ietf.org/html/rfc7049">Concise Binary Object Representation (CBOR)</a>, 2013.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
</div>
<div id="footnotes">
<hr>
<div class="footnote" id="_footnotedef_1">
<a href="#_footnoteref_1">1</a>. This padding algorithm is apparently also specified in ISO/IEC 7816-4. However, the speicifcation is not openly available. So, fuck you ISO.
</div>
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