extra-seed

#!/usr/bin/env python3
# Generate a hash chain from a seed.
# By Martin Thomson, posted to IETF eligibilty-discuss at
#   https://mailarchive.ietf.org/arch/msg/eligibility-discuss/xH7C0amrezjq-p3aMeF3h01S3I0/
# "For now, I'll share the code I used to generate it.  The value published
# is on line 25 of the output.  I'll use line 24 first, if necessary, then 23,
# and so on.  Hopefully I won't need too many, but if we have extraordinary bad
# luck and things drag on, then public randomness might be needed.  I consider
# that unlikely, but Rich had three people decline or fail to answer, so a few
# rounds seems entirely possible."
import hashlib
import sys

count = 25

if len(sys.argv) < 2:
    print(f"Usage: {sys.argv[0]} <seed string>")
    exit(2)

input = sys.argv[1]
if not input.isascii():
    print("Supplied string is not ASCII")
    exit(2)

print(f"input[{len(input)}]: '{input}'")
b = input.encode('ascii')
print(f" 0: {b.hex()}")
x = hashlib.sha256(b)
for i in range(1,count):
    print(f"{i:>2}: {x.hexdigest()}")
    x = hashlib.sha256(x.digest())

print(f"{count:>2}: {x.hexdigest()}")