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<a href="https://gitlab.com/vivien_">Vivien Kraus Would Rather Not Be On Gitlab.com</a>
commented on a
<a href="https://gitlab.com/gnutls/guile/-/issues/13#note_1475344062">discussion</a>:
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<p dir="auto" style="color: #333238; margin: 0 0 16px;" align="initial">I’m not sure how it works, I tried to concatenate the "digest" with the "encrypt" result (after an "update") but it does not give the correct result. I must be missing something. I guess the nonce value should not be used as an initialization vector…</p>
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<pre data-canonical-lang="c" class="code highlight js-syntax-highlight language-c" lang="c" v-pre="true" style='display: block; font-size: 14px; color: #333238; line-height: 1.6em; overflow-x: auto; border-radius: 4px; position: relative; font-family: var(--default-mono-font, "GitLab Mono"),"JetBrains Mono","Menlo","DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 16px; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: 0.875rem; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: 4px; white-space: pre; margin-top: 0; font-family: var(--default-mono-font, "GitLab Mono"),"JetBrains Mono","Menlo","DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="c" style="margin-top: 0;"><span class="cp" style="margin-top: 0;">#include</span> <span class="cpf"><nettle/gcm.h></span></span>
<span id="LC2" class="line" lang="c"><span class="cp" style="margin-top: 0;">#include</span> <span class="cpf"><stdlib.h></span></span>
<span id="LC3" class="line" lang="c"><span class="cp" style="margin-top: 0;">#include</span> <span class="cpf"><stdio.h></span></span>
<span id="LC4" class="line" lang="c"><span class="cp" style="margin-top: 0;">#include</span> <span class="cpf"><string.h></span></span>
<span id="LC5" class="line" lang="c"></span>
<span id="LC6" class="line" lang="c"><span class="kt" style="margin-top: 0;">int</span></span>
<span id="LC7" class="line" lang="c"><span class="nf" style="margin-top: 0;">main</span> <span class="p">()</span></span>
<span id="LC8" class="line" lang="c"><span class="p" style="margin-top: 0;">{</span></span>
<span id="LC9" class="line" lang="c"> <span class="k" style="margin-top: 0;">static</span> <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">key</span> <span class="o">=</span> <span class="s">"the secret key is 32 bytes long."</span><span class="p">;</span></span>
<span id="LC10" class="line" lang="c"> <span class="k" style="margin-top: 0;">static</span> <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">auth</span> <span class="o">=</span> <span class="s">"Additional secret data"</span><span class="p">;</span></span>
<span id="LC11" class="line" lang="c"> <span class="k" style="margin-top: 0;">static</span> <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">nonce</span> <span class="o">=</span> <span class="s">"Never encrypt more data with this nonce"</span><span class="p">;</span></span>
<span id="LC12" class="line" lang="c"> <span class="k" style="margin-top: 0;">static</span> <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">data</span> <span class="o">=</span> <span class="s">"Confidential data."</span><span class="p">;</span></span>
<span id="LC13" class="line" lang="c"> <span class="k" style="margin-top: 0;">struct</span> <span class="n">gcm_aes256_ctx</span> <span class="n">context</span><span class="p">;</span></span>
<span id="LC14" class="line" lang="c"> <span class="n" style="margin-top: 0;">gcm_aes256_set_key</span> <span class="p">(</span><span class="o">&</span><span class="n">context</span><span class="p">,</span> <span class="n">key</span><span class="p">);</span></span>
<span id="LC15" class="line" lang="c"> <span class="n" style="margin-top: 0;">gcm_aes256_set_iv</span> <span class="p">(</span><span class="o">&</span><span class="n">context</span><span class="p">,</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">nonce</span><span class="p">),</span> <span class="n">nonce</span><span class="p">);</span></span>
<span id="LC16" class="line" lang="c"> <span class="k" style="margin-top: 0;">static</span> <span class="k">const</span> <span class="kt">size_t</span> <span class="n">tag_size</span> <span class="o">=</span> <span class="mi">16</span><span class="p">;</span></span>
<span id="LC17" class="line" lang="c"> <span class="kt" style="margin-top: 0;">size_t</span> <span class="n">used_size</span> <span class="o">=</span> <span class="n">tag_size</span> <span class="o">+</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">data</span><span class="p">);</span></span>
<span id="LC18" class="line" lang="c"> <span class="kt" style="margin-top: 0;">char</span> <span class="n">output</span><span class="p">[</span><span class="n">used_size</span><span class="p">];</span></span>
<span id="LC19" class="line" lang="c"> <span class="n" style="margin-top: 0;">gcm_aes256_update</span> <span class="p">(</span><span class="o">&</span><span class="n">context</span><span class="p">,</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">auth</span><span class="p">),</span> <span class="n">auth</span><span class="p">);</span></span>
<span id="LC20" class="line" lang="c"> <span class="n" style="margin-top: 0;">gcm_aes256_encrypt</span> <span class="p">(</span><span class="o">&</span><span class="n">context</span><span class="p">,</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">data</span><span class="p">),</span> <span class="o">&</span> <span class="p">(</span><span class="n">output</span><span class="p">[</span><span class="n">tag_size</span><span class="p">]),</span> <span class="n">data</span><span class="p">);</span></span>
<span id="LC21" class="line" lang="c"> <span class="n" style="margin-top: 0;">gcm_aes256_digest</span> <span class="p">(</span><span class="o">&</span><span class="n">context</span><span class="p">,</span> <span class="n">tag_size</span><span class="p">,</span> <span class="n">output</span><span class="p">);</span></span>
<span id="LC22" class="line" lang="c"> <span class="k" style="margin-top: 0;">for</span> <span class="p">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">used_size</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span></span>
<span id="LC23" class="line" lang="c"> <span class="n" style="margin-top: 0;">fprintf</span> <span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"%x "</span><span class="p">,</span> <span class="mh">0xFF</span> <span class="o">&</span> <span class="n">output</span><span class="p">[</span><span class="n">i</span><span class="p">]);</span></span>
<span id="LC24" class="line" lang="c"> <span class="k" style="margin-top: 0;">if</span> <span class="p">(</span><span class="n">output</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">!=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span> <span class="mi">165</span><span class="p">)</span></span>
<span id="LC25" class="line" lang="c"> <span class="p" style="margin-top: 0;">{</span></span>
<span id="LC26" class="line" lang="c"> <span class="k" style="margin-top: 0;">return</span> <span class="n">EXIT_FAILURE</span><span class="p">;</span></span>
<span id="LC27" class="line" lang="c"> <span class="p" style="margin-top: 0;">}</span></span>
<span id="LC28" class="line" lang="c"> <span class="n" style="margin-top: 0;">fprintf</span> <span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"OK</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span></span>
<span id="LC29" class="line" lang="c"> <span class="k" style="margin-top: 0;">return</span> <span class="n">EXIT_SUCCESS</span><span class="p">;</span></span>
<span id="LC30" class="line" lang="c"><span class="p" style="margin-top: 0;">}</span></span></code></pre>
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