Communication with Extraterrestrial Intelligence — by Lambros D. Callimahos (NSA Cryptologic Spectrum)

Brief

Published in the NSA's internal Cryptologic Spectrum journal and originally delivered as a Cosmos Club lecture, this paper by Lambros D. Callimahos opens with the unqualified assertion 'We are not alone in the universe' and surveys the mainstream scientific case for extraterrestrial intelligence, citing the National Academy of Sciences, Drake's estimate of one billion galactic civilizations, and Shklovsky's taxonomy of civilization-ending crises including 'the creation of artificial intelligent beings.' Callimahos then reframes SETI as a cryptanalytic challenge — rather than classical cryptography, which hides meaning, the needed discipline is 'inverse cryptography,' communication symbolism designed to be maximally comprehensible to an unknown recipient. He illustrates this with a hypothetical 30-transmission alien exchange, building from symbol enumeration through arithmetic to Euler's identity, and closes by warning the future cryptologist to keep a level head when contact arrives.

Metadata

Agency

National Security Agency

Release

1966-01-01

Type

PDF • .pdf

Length

7 pages

Classification

FOR OFFICIAL USE ONLY (FOUO)

Programs

Project Ozma, Lincos

Tags

ETI communication, SETI, radio astronomy, inverse cryptography, Arecibo message, hydrogen line 1420 MHz, Fermat conjecture, fine structure constant, Cosmos Club lecture, Cryptologic Spectrum journal

Key points

• Callimahos opens with the unqualified statement 'We are not alone in the universe,' citing the National Academy of Sciences and leading radio astronomers — not as speculation but as established scientific consensus.p.1
• Frank Drake estimated approximately one billion civilizations may have arisen in the observable universe; Sir Bernard Lovell calculated roughly 100 million stars in the Milky Way alone with conditions suitable for organic evolution, 'even allowing for a margin of error of 5000%.'p.1
• Shklovsky enumerated five crises capable of destroying any developing civilization, including thermonuclear catastrophe, genetic danger, information overload, brain-capacity limits leading to degeneration, and 'a crisis precipitated by the creation of artificial intelligent beings.'p.1
• Project Ozma (1960) tuned to the 1420.4057 megacycle hydrogen-line frequency and monitored Epsilon Eridani and Tau Ceti — the first systematic radio search for extraterrestrial signals, justified because the hydrogen frequency 'would be known to other intelligent beings in the universe who understand radio theory.'p.2
• In November 1974, Arecibo Observatory beamed a three-minute binary message toward Messier 13, 24,000 light years away — described as 'man's first attempt to take the initiative in communicating with another civilization,' with an expected reply time of 48,000 years.p.2
• Bernard Oliver's 1,271-bit hypothetical pictogram encodes a solar system map, bisexual mammalian beings pointing to the fourth planet, hydrogen/carbon/oxygen chemistry, a fish Callimahos interprets as evidence the senders 'must have visited us and therefore have space travel,' and beings approximately 7.5 feet tall.p.4
• Callimahos coins 'inverse cryptography' for the design of communication symbolism intended not to hide meaning but to be as transparent as possible to a recipient 'whose thinking processes may be entirely different from our own,' making sender cleverness the critical variable rather than recipient ingenuity.p.4
• Freudenthal's 1960 'Lincos' (lingua cosmica) is assessed as 'too difficult' by general consensus; Callimahos's own 30-transmission hypothetical bootstraps from symbol enumeration through arithmetic, inequalities, powers, infinite series, and Euler's identity before reaching word-cluster and sentence-level concepts.p.4
• Knowing the seventh digit of the fine structure constant (137.039...) is offered as a concrete benchmark of civilizational superiority: 'if they but know the seventh digit of the fine structure constant, they are ages ahead of us (we know only the first five for sure, suspect the sixth).'p.6
• The paper closes by warning that the cryptologist must 'keep a level head, not get excited, and be prepared to cope with problems the likes of which he has never seen' — framing first contact as above all a professional challenge for the intelligence community.p.7

Verbatim

• We are not alone in the universe.

  p.1

• Even the staid National Academy of Sciences has gone on record that contact with other civilizations "is no longer something beyond our dreams but a natural event in the history of mankind that will perhaps occur in the lifetime of many of us."

  p.1

• Dr. Frank D. Drake of the National Radio Astronomy Observatory at Green Bank, West Virginia, has stated that, putting all our knowledge together, the number of civilizations which could have arisen by now is about one billion.

  p.1

• Cleverness on the part of the sender is then the important factor, not reliance on ingenuity of the recipient.

  p.4

• Transmission (21) adds nothing new to the 31 symbols recovered thus far, but it does quote one of the most beautiful concepts in pure mathematics, Euler's identity, e;. + 1 = 0. With this they are telling us that, if they can teach us such a complex notion at this early stage, we will be staggered by what they will teach us by the 200th or 2000th transmission.

  p.4

Most interesting

• Callimahos was a world-renowned flute virtuoso before his wartime cryptology career and subsequently taught NSA's senior cryptanalysis course for twenty years — making him simultaneously the intelligence community's top codebreaker and a concert-level musician.
• The paper references a 1971 six-nation conference on extraterrestrial communication held in Soviet Armenia, co-attended by Carl Sagan — a US-Soviet scientific forum on ETI that received almost no public attention and is omitted from most SETI histories.
• The full binary grid of the 1974 Arecibo transmission appears in the document as Figure 1, occupying most of page 2 — one of the very few times an actual interstellar radio transmission has been reproduced inside an NSA publication.
• Callimahos interprets the fish symbol in Oliver's hypothetical alien pictogram as proof that the senders 'must have visited us and therefore have space travel' — a striking inferential leap embedded without caveat in a classified intelligence journal.
• Shklovsky's fifth civilizational crisis — 'a crisis precipitated by the creation of artificial intelligent beings' — is listed matter-of-factly alongside thermonuclear catastrophe in a mid-1970s NSA document, decades before AI risk became a mainstream concern.
• Callimahos suggests that a superior civilization might modulate neutrino beams as a communication medium but concedes humanity 'may have to wait a century or two before we learn how to build a neutrino receiver' — a technically credible observation that anticipated modern neutrino-detector physics.
• The paper identifies potential communication media beyond radio: masers, lasers, and a speculative unnamed technology Callimahos calls 'rasers' — a placeholder for whatever comes next on the electromagnetic spectrum.
• The war.gov listing dates this document to 1966-01-01, but internal references to the November 1974 Arecibo transmission and the 1973 MIT publication of the Soviet Armenia conference proceedings place authorship no earlier than early 1975, suggesting a metadata error in the release record.