user78997: From an example in the documentation:
$ bx seed | bx mnemonic-new | bx mnemonic-to-seed | bx hd-new

655a1ed2d4fef69bb314198c7327f23c
grab special regret prepare urge evidence slush lobster midnight odor wish ketchup
57bae342ae8e69eb63f17ef993a90a59159e0f78114b602bf0ebabfec0e5d086e883c31975bf03f8a47a32853452623094d1303fd0549745db457145e5756582
xprv9s21ZrQH143K43CUCgNp5SmXzg2axQx2P4WupA2zEnKpFM19QfqfdqfpJR3yfzAXZnsHeUaQhWQMwyuqL8DbdeLeCbdMoKNn6pCY4RUn2pK
In Mastering Bitcoin, the example given here shows it going back to the seed that was originally created; this was done using an older version of bx though. Can someone explain how the seeds from line 1 and line 3 in the example are encoded/related?

user132451: Fundamental flaw here, multiple meanings of the word "seed"even within discussion of just BIP39.
The "entropy" is a better term for the BIP39 starting point. Then the endpoint of the process should be "BIP39 numeric seed".

"Convert the entropy to a BIP39 mnemonic. Use that mnemonic plus a (technically optional but no) passphrase as the inputs to produce the BIP39 numeric seed. End of BIP39. "

is how I would tell the story.
Now, looking at this from *Mastering Bitcoin *

The seed can be encoded using the mnemonic-encode command:


$ bx hd-mnemonic < seed > words
adore repeat vision worst especially veil inch woman cast recall dwell appreciate


The seed can then be decoded using the mnemonic-decode command:


$ bx mnemonic-decode < words
eb68ee9f3df6bd4441a9feadec179ff1

Andreas Antonopoulos is here clearly using "seed" to refer to the entropy. The process described does not involve hashing, or cryptographic "encoding", it's just a change in representation, like going from binary to hex.
Except for the N/32 checksum getting added.
Which means an input entropy of 256 bits is entirely reversible, but the last 8 bits to get to 264 (24 words x 11 bits) is the result of the checksum process.
What the other answers here are referring to is not the "entropy seed" but the output, the "BIP39 numeric seed" which is indeed a one way derivation process.
I believe the bx mnemonic-decode command may have gotten removed simply because it is useless, or at least I cannot think of a use case.
I do not think it stopped working in the transition to BIP39. EDIT The entropy to mnemonic "conversion" is reversed by many tools - see https://iancoleman.app

78997: <p>From an example in the <a href="https://github.com/libbitcoin/libbitcoin-explorer/wiki/bx-mnemonic-to-seed" rel="nofollow noreferrer">documentation</a>:</p>

<pre><code>$ bx seed | bx mnemonic-new | bx mnemonic-to-seed | bx hd-new
</code></pre>

<p><code>655a1ed2d4fef69bb314198c7327f23c
grab special regret prepare urge evidence slush lobster midnight odor wish ketchup
57bae342ae8e69eb63f17ef993a90a59159e0f78114b602bf0ebabfec0e5d086e883c31975bf03f8a47a32853452623094d1303fd0549745db457145e5756582
xprv9s21ZrQH143K43CUCgNp5SmXzg2axQx2P4WupA2zEnKpFM19QfqfdqfpJR3yfzAXZnsHeUaQhWQMwyuqL8DbdeLeCbdMoKNn6pCY4RUn2pK</code></p>

<p>In Mastering Bitcoin, the example given <a href="https://github.com/bitcoinbook/bitcoinbook/blob/develop/appdx-bx.asciidoc" rel="nofollow noreferrer">here</a> shows it going back to the seed that was originally created; this was done using an older version of bx though. Can someone explain how the seeds from line 1 and line 3 in the example are encoded/related?</p>
 132451: <p>Fundamental flaw here, multiple meanings of the word &quot;seed&quot;even within discussion of just BIP39.</p>
<p>The &quot;entropy&quot; is a better term for the BIP39 starting point. Then the endpoint of the process should be &quot;BIP39 numeric seed&quot;.</p>
<blockquote>
<p>&quot;Convert the entropy to a BIP39 mnemonic. Use that mnemonic plus a (technically optional but no) passphrase as the inputs to produce the BIP39 numeric seed. End of BIP39. &quot;</p>
</blockquote>
<p>is how I would tell the story.</p>
<p>Now, looking at this from *Mastering Bitcoin *</p>
<blockquote>
<p>The seed can be encoded using the mnemonic-encode command:</p>
</blockquote>
<blockquote>
<p>$ bx hd-mnemonic &lt; seed &gt; words
adore repeat vision worst especially veil inch woman cast recall dwell appreciate</p>
</blockquote>
<blockquote>
<p>The seed can then be decoded using the mnemonic-decode command:</p>
</blockquote>
<blockquote>
<p>$ bx mnemonic-decode &lt; words
eb68ee9f3df6bd4441a9feadec179ff1</p>
</blockquote>
<p>Andreas Antonopoulos is here clearly using &quot;seed&quot; to refer to the entropy. The process described does not involve hashing, or cryptographic &quot;encoding&quot;, it's just a change in representation, like going from binary to hex.</p>
<p>Except for the N/32 checksum getting added.</p>
<p>Which means an input entropy of 256 bits is entirely reversible, but the last 8 bits to get to 264 (24 words x 11 bits) is the result of the checksum process.</p>
<p>What the other answers here are referring to is not the &quot;entropy seed&quot; but the output, the &quot;BIP39 numeric seed&quot; which is indeed a one way derivation process.</p>
<p>I believe the <code>bx mnemonic-decode</code> command may have gotten removed simply because it is useless, or at least I cannot think of a use case.</p>
<p>I do not think it stopped working in the transition to BIP39. <strong>EDIT</strong> The entropy to mnemonic &quot;conversion&quot; is reversed by many tools - see <a href="https://iancoleman.app" rel="nofollow noreferrer">https://iancoleman.app</a></p>
