user50901: I have a random private key (compressed or uncompressed) 5HpHagT65TZzG1QDbnQCzdudnpknN7nA1SLEt4ZcxsH2SV92yqt or KwDiBf89QgGbjEmUcXPRwPuKPFnFECvJkvovGNiyjaujMCrQXy98. How do I convert this private key back to an integer?

user87716: Assuming the key is the posted  compressed WIF KwDiBf89QgGbjEmUcXPRwPuKPFnFECvJkvovGNiyjaujMCrQXy98:   

Decode the key you have using the encoder used (in this case base-58)
80-00000000000000000006f5d7d806edef2e1110b0b243f9a90c2aaaaaaaaaaaaa-01-098dbf37
Remove the extra bytes (version byte, compressed byte if present, checksum)
00000000000000000006f5d7d806edef2e1110b0b243f9a90c2aaaaaaaaaaaaa
Take the remaining bytes (in this case it must be 32 bytes) and convert it to an integer assuming it is positive and in big-endian (most significant value is stored first).
666666666666666666666666666666666666666666666666666666


50901: <p>I have a random private key (compressed or uncompressed) <code>5HpHagT65TZzG1QDbnQCzdudnpknN7nA1SLEt4ZcxsH2SV92yqt</code> or <code>KwDiBf89QgGbjEmUcXPRwPuKPFnFECvJkvovGNiyjaujMCrQXy98</code>. How do I convert this private key back to an integer?</p>
 87716: <p>Assuming the key is the posted  compressed WIF <code>KwDiBf89QgGbjEmUcXPRwPuKPFnFECvJkvovGNiyjaujMCrQXy98</code>:   </p>

<ol>
<li>Decode the key you have using the encoder used (in this case <a href="https://en.bitcoin.it/wiki/Base58Check_encoding" rel="noreferrer">base-58</a>)<br>
<code>80-00000000000000000006f5d7d806edef2e1110b0b243f9a90c2aaaaaaaaaaaaa-01-098dbf37</code></li>
<li>Remove the <a href="https://en.bitcoin.it/wiki/Wallet_import_format" rel="noreferrer">extra bytes</a> (version byte, compressed byte if present, checksum)<br>
<code>00000000000000000006f5d7d806edef2e1110b0b243f9a90c2aaaaaaaaaaaaa</code></li>
<li>Take the remaining bytes (in this case it must be 32 bytes) and convert it to an integer assuming it is positive and in <a href="https://en.wikipedia.org/wiki/Endianness" rel="noreferrer">big-endian</a> (most significant value is stored first).<br>
<code>666666666666666666666666666666666666666666666666666666</code></li>
</ol>
