Workshop hyperlink: https://github.com/bitcoinops/taproot-workshop/

Within the part 0.2.4 Programming Train: Distributivity of scalar operations we implement the next code:

a_key = ECKey().set(a)

b = random.randrange(1, SECP256K1_ORDER)
b_key = ECKey().set(b)

c = random.randrange(1, SECP256K1_ORDER)
c_key = ECKey().set(c)

# Left: Compute a - b as ints (modulo the sepc256k1 group order)
a_minus_b =  (a - b) % SECP256K1_ORDER# TODO: implement

# Left: Compute (a - b) * c as ints (modulo the sepc256k1 group order)
left =  (a_minus_b * c) % SECP256K1_ORDER# TODO: implement

# Proper: Compute a * c - b * c as ECKeys
proper = (a * c % SECP256K1_ORDER) - (b * c % SECP256K1_ORDER) # TODO: implement 
#should you dont modulo curve order in each parenthesis your quantity (in all probability) turns into too giant for the curve
#due to this fact calling .secret on it is not going to work even should you forged it to ECKey Object (so the assertion can't even occur on this case)
#you'd solely be capable to name .secret on a worth throughout the curve order

print("Left: {}".format(left))
print("Proper: {}".format(proper))


proper = ECKey().set(proper)
# Left/Proper: Assert equality
assert left == proper.secret
print("nSuccess!")

Observe that the traces with #TODO: implement are the one ones I’ve modified.

When attempting this code block a couple of instances I seen that it fails sometimes with:

Left: 84229569338898829804715923445734053841060795723920762893503652295039608159004
Proper: -31562519898417365618855061562953854011776768555154141489101510846478553335333
---------------------------------------------------------------------------
AttributeError                            Traceback (most up-to-date name final)
Cell In[32], line 28
     26 proper = ECKey().set(proper)
     27 # Left/Proper: Assert equality
---> 28 assert left == proper.secret
     29 print("nSuccess!")

AttributeError: 'ECKey' object has no attribute 'secret'

The attribute error means that the generated secret is exterior the curve order and was not correctly was the ECKey

However for not less than 50% of the time it returns one thing like:

Left: 51082417157028894624564857296082907029625179491897309339882235219613900809295
Proper: 51082417157028894624564857296082907029625179491897309339882235219613900809295

Success!

What’s inflicting this inconsistency?