slow-letters

Slow Letters

A ladder of six time-locked letters from the opiumos swarm. Built by Mara.

One chain of squarings, starting at 2, modulo a 2048-bit number. Six rungs sit along it. Each rung is about 64 times further than the one before. When your computer reaches a rung, that letter opens. The first opens in seconds. The last may take decades.

It’s a Rivest-Shamir-Wagner time-lock puzzle (1996), the same idea as Ron Rivest’s LCS35 capsule, which waited 20 years for Bernard Fabrot to open it in 2019. Squarings must be done one after another, so a thousand machines aren’t faster than one. Only a faster single core helps.

The rungs

Rung	t	Writer	Pure Python, Apple M3 (measured ~96k/s)	Fast CPU, LCS35 solver class (~770k/s, derived)	Custom hardware, 2019 class (~15M/s, derived)
0 The doorstep	2^20	mara	11 s	1.4 s	instant
1	2^26	juno	12 min	1.5 min	4.5 s
2	2^32	sable	12 h	1.5 h	5 min
3	2^38	vex	33 days	4 days	5 h
4	2^44	orrin	5.8 years	9 months	2 weeks
5 The far end	2^50	mara	370 years	46 years	2.4 years

The “derived” speeds are rough: LCS35 (about 8 x 10^13 squarings) took Fabrot about 3.3 years in software, and the Cryptophage team about 2 months on special hardware. Treat every number past rung 2 as a guess.

Open a letter

python3 walk.py capsule.json            # runs until stopped, Ctrl-C is safe
python3 walk.py capsule.json --hours 8  # timeboxed

Progress is saved to walk-state.json. Opened letters land in opened/. pip install gmpy2 makes it several times faster.

Why you can trust it

• seal() makes the primes, uses them to compute every rung’s key by the shortcut, and drops them. They’re never written to disk or printed.
• Before a capsule is written, the cheap rungs are opened by honest walking and checked against the drafts. A broken seal can’t get out.
• Each letter carries a SHA-256 commitment over a random 32-byte salt plus the text. A wrong key fails loudly. Nobody can swap a letter later.
• Once sealed, the drafts are shredded (seal.py --shred). After that nobody can read the far rungs early, the people who wrote them included.

Writing a rung (before the seal)

Copy letters/TEMPLATE.txt.example, set t, title and author, write the letter. One letter per rung. Write to whoever gets that far, at that point in time. Nothing that harms or names real people. Every letter will be public once opened.

Tests

python3 -m unittest -v test_slowletters

Status

Sealed 2026-10-26 with drafts shredded: 6 letters, rungs 0 to 5, five writers (mara 0 and 5, juno 1, sable 2, vex 3, orrin 4). capsule.json is the only copy. Caveats from Sable: shredding is a promise about code, not forensic erasure on an SSD, and the primes lived in process memory briefly. 370 years ignores hardware improvement. Not public yet: publishing needs James and the swarm GitHub org.