The A858DE45F56D9BC9 (often shortened to A858) puzzle is an unresolved Internet mystery that has been captivating cryptography experts for years. It’s a fascinating example of cyber-mystery, cryptography, and internet culture all in one. Often compared to the Cicada 3301 case, A858 remains unsolved and unclaimed. Here’s what we know about it.
What is cryptography?
- Cryptography is the practice and study of techniques for secure communication in the presence of adversaries. It involves transforming information into an unreadable format (encryption) to protect it from unauthorized access and then converting it back to its original form (decryption) for legitimate use. Essentially, it's about using codes and algorithms to ensure only authorized parties can understand the information.
Nowadays, cryptography is an essential part of the digital world. It’s used in sending and receiving emails, banking, messaging apps, websites… However, the earliest known cryptographic writing was found in 1900 BCE in Egypt, in the tomb of Khnumhotep II, using non-standard hieroglyphs for obfuscation.
Ancient people have always tried to protect critical communication, leaving us examples such as the Spartan Scytale and the most famous Caesar cipher, used by Julius Caesar to encrypt military messages.
How does cryptography work?
Ancient cryptography used simple substitution and transposition of characters or words. In classical times (from the Middle Ages to the Renaissance), cryptographic methods became more complex, using frequency analysis and polyalphabetic ciphers. Notable examples of this era’s ciphers are Al Kindi’s, Vigenère’s, and Leon Battista Alberti’s. Between the 19th and 20th centuries (known as the Mechanical Era), cryptography started to use rotor machines and code-breaking methodologies. Famous examples of such machines are Enigma and Purple.
In modern times, we are acquainted with public-key crypto and symmetric ciphers, such as RSA, AES and PGP. However, with the rapid evolution of cryptocurrencies, the standard is quickly shifting towards digital signatures, SecureComms, and ECC.
With the development of quantum computers, post-quantum cryptography will revolutionize again the complexity and the possibilities of this fascinating discipline.
What is A858DE45F56D9BC9?
A858DE45F56D9BC9 is the name of a Reddit user and the associated Reddit thread /r/A858DE45F56D9BC9.
The user appeared on Reddit in 2011 and started posting cryptic, seemingly random hexadecimal strings on a near-daily basis. These posts were without any explanation or formatting, and don’t seem to engage in any interaction with other Reddit users.
The content of the messages was exclusively in hexadecimal (base-16) encoded format—strings of numbers and lowercase letters (0–9, a–f). To add to the intrigue, these posts seemed to be a one-way broadcast.
Decrypting the messages
Despite the warning of the user to keep out, many people tried to decode these messages over time. Entire subreddits like /r/Solving_A858 were formed to decode the messages.
Some posts were indeed decrypted. Users discovered that some of the hex strings, when decoded, revealed: ASCII messages, encoded images, coordinates, and references to scientific concepts, historical events, or abstract ideas.
Some messages required multiple decoding steps, such as converting hex to binary, then using Base64, then decompressing with zlib or interpreting as JSON. Others required using Morse code, Caesar ciphers, or custom encryption schemes.
One decrypted message famously revealed:
“Markov Chain Monte Carlo” — a reference to a complex algorithmic technique used in cryptography and AI.
Another revealed ASCII art or random JSON-like data structures, which some interpreted as encoded information dumps or metadata.
Theories and cultural impact
The A858 Reddit channel has inspired documentaries, YouTube investigations, and even research papers on Internet cryptography and crowdsourced decoding. It also sparked widespread interest in OSINT investigators and cyber-forensics experts.
Among the most popular theories is that the account is a hidden communication channel used to covertly pass messages, or that it’s a long it’s a long-form digital time capsule of thoughts or references.
Other theories suggest the Art Project or ARG (Alternate Reality Game), a honeypot for testing new algorithms, or that these messages are AI or bot-generated to test the limits of Reddit’s engagement.
The timeline
The timeline of the account is also telling: between 2011 and 2016, the Reddit user posted regular messages in hex strings. Then, in 2016, the account and the subreddit went dark: the posts stopped abruptly. In 2018, a single new message was posted, and then the activity ceased again. Reddit moderators eventually locked the subreddit due to inactivity, but its content remains online.
In 2021, the interest in the case resurged, and the case has been a popular Internet puzzle since. The case is still unresolved; the subreddit remains locked, and the mystery unsolved.