user4023: What equation suitable for generation of a public key is used for Edwards curve Ed25519?
The problem is the following – info on Edwards Elliptic Curve on Wikipedia page presents an equation y^2 + x^2 = 1 + d * y^2 * x^2 that doesn't allow us to plot a curve depicted on the first picture.
So, what equation is used for Ed25519? This one?
y^2 + x^2 = 1 - d * y^2 * x^2


Or this one?
y^2 + x^2 = 1 + d * y^2 * x^2


I haven't found any documentation covering this topic.

user12: The general equation of the Edwards curve is

for Ed25519
a = -1, d = -121665/121666.
The curve is also living in the prime field. The equation is 
I could not plot this equation in geograba, I guess due to the nature of the prime field over which the equation is defined.(?)

4023: <p>What equation suitable for generation of a public key is used for Edwards curve <code>Ed25519</code>?</p>
<p>The problem is the following – info on <a href="https://en.wikipedia.org/wiki/Edwards_curve" rel="nofollow noreferrer">Edwards Elliptic Curve</a> on Wikipedia page presents an equation <code>y^2 + x^2 = 1 + d * y^2 * x^2</code> that doesn't allow us to plot a curve depicted on the first picture.</p>
<p>So, what equation is used for <code>Ed25519</code>? <strong>This one?</strong></p>
<pre><code>y^2 + x^2 = 1 - d * y^2 * x^2
</code></pre>
<p><a href="https://i.stack.imgur.com/nFN2a.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nFN2a.png" alt="enter image description here" /></a></p>
<p><strong>Or this one?</strong></p>
<pre><code>y^2 + x^2 = 1 + d * y^2 * x^2
</code></pre>
<p><a href="https://i.stack.imgur.com/uDn3V.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uDn3V.png" alt="enter image description here" /></a></p>
<p>I haven't found any documentation covering this topic.</p>
 12: <p>The general equation of the Edwards curve is</p>
<p><img src="https://latex.codecogs.com/svg.image?ax%5E2%20+%20y%5E2%20=%201%20+%20dx%5E2y%5E2" alt="ax^2 + y^2 = 1 + dx^2y^2" /></p>
<p>for Ed25519
a = -1, d = -121665/121666.</p>
<p>The curve is also living in the prime field. The equation is <a href="https://i.stack.imgur.com/qSOC0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qSOC0.png" alt="enter image description here" /></a></p>
<p>I could not plot this equation in geograba, I guess due to the nature of the prime field over which the equation is defined.(?)</p>
