Jan Liseiwicz’s Letters to Jinzhen Warning Him Against Cryptography

Jan Liseiwicz’s Letters to Jinzhen Warning Him Against Cryptography form a failed exchange between a former teacher and student, and an intercepted correspondence that Unit 701 converts into an intelligence operation. Liseiwicz writes out of affection and alarm, urging Rong Jinzhen to return to Artificial intelligence research and warning that cryptography can entrap and damage those who enter it. But the letters never reach Rong Jinzhen. Instead, the Party reads them, answers in his name, and uses Liseiwicz’s concern to seek help with the PURPLE cipher.

The first appeal

After meeting Master Rong, Liseiwicz repeatedly asks her to tell Rong Jinzhen to put aside other temptations and resume his Artificial intelligence work. Once she has left, he realizes that he has no way to contact Jinzhen directly, calls after Master Rong to ask for his address, and writes that evening. Before posting it, he shows the letter to his own guard and the Chinese guard and obtains permission from both. The circumstances already place private concern inside systems of permission and surveillance.

The letter is dated 13 March 1957. It fills a sheet in English but, when translated into Chinese, amounts to only a couple of lines. Liseiwicz explains that he has returned to China at his mother-in-law’s request and is staying in the provincial capital. He has heard that Jinzhen has left the university for secret work; the secrecy surrounding both the work and the address makes him suspect that his former student has joined a top-secret unit, as Liseiwicz himself once did.

Liseiwicz connects his warning to his own experience. He says that, out of sympathy and love for his people, he accepted a mission entrusted to him by a country ten years earlier, and that the decision ruined his life. He fears that Jinzhen’s acute but fragile intelligence will be exposed to external pressure and control. Against that prospect, he sets the promise of Jinzhen’s existing research: he believes that continuing in Artificial intelligence could bring him recognition and urges him not to be diverted from that work.

A warning about cryptography

Unit 701’s surveillance team receives the letter through the ordinary mail route, but personal correspondence is inspected there. Its English text immediately alarms the readers, who report it and request a translation. Because its contents are judged unhealthy, Jinzhen is not allowed to see it. The unit’s rule against asking, discussing, or investigating forbidden matters gives officials a ready way to suppress the letter, but the suppression does not stop Liseiwicz from trying again.

About a month later, another letter arrives from X Country. It is longer, also in English, and again urges Jinzhen to return to his original research. Liseiwicz says a dream prompted him to write: in it, Jinzhen tells him that he has become a cryptographer in a top-secret unit. Liseiwicz admits that he cannot interpret dreams or know whether this one corresponds to reality, but he treats it as an expression of his own hopes and fears. His anxiety is sharpened by Jinzhen’s silence, his talent, and the apparent change in his work.

The letter argues that cryptography is fundamentally opposed to scientific and intellectual life. Liseiwicz sees ciphers as concealed warfare: success does not end conflict but presses others to become more cunning, and the struggle yields no worthwhile victory. His warning is not simply that Jinzhen may find the work difficult. He believes the field itself can isolate and ensnare the people who touch it, making a professional assignment into a kind of confinement.

The forbidden cipher

Liseiwicz’s most pointed instruction concerns the PURPLE cipher. He tells Jinzhen that if returning to his former work is impossible, he may have to decrypt other ciphers, but must not work on PURPLE. At Unit 701, that warning carries particular weight. PURPLE is described as the most difficult cipher the unit has been tasked to break; its elaborate procedures and nested internal ciphers have resisted the cryptography division for years. The group is desperate to solve it, yet experience has made its members increasingly afraid to approach it. The mathematician said to have created it went mad, reinforcing the sense that the cipher is a trap as well as a technical challenge.

The specificity of Liseiwicz’s warning changes how Unit 701 reads the letters. His knowledge of the danger suggests that he may know something about how PURPLE works, while the closeness between him and Jinzhen offers a possible route to that knowledge. The warning intended to protect a former student is thus recast as an opportunity: officials decide to test whether Liseiwicz’s affection can be used to elicit advice.

Forged replies and the bait

Unit 701 sends Liseiwicz a typed letter bearing a forged handwritten signature in Jinzhen’s name. Five experts prepare the first draft, and three directors approve it. Its central question asks why Jinzhen cannot decrypt PURPLE. The letter’s respectful tone is strategic, not evidence of Jinzhen’s own participation: he remains unaware of the correspondence and is not the author of the reply attributed to him.

Liseiwicz answers quickly. In the next fabricated message, Unit 701’s false Jinzhen claims to have lost his freedom and says that decrypting PURPLE is necessary to regain it. The plea asks for pointers and presents its supposed writer as ashamed to seek help. Because the message cannot safely be posted directly, it is routed through comrades in X Country for private delivery. The operation is uncertain: the officials understand that the apparent betrayal might disgust Liseiwicz as readily as it might move him.

It moves him. For the following six months, Liseiwicz repeatedly risks being treated as a traitor by contacting the intermediaries and sending material about PURPLE, along with suggestions for how to proceed. Unit 701 responds by forming a temporary PURPLE decryption working group, staffed largely by its cryptographers. The irony is stark: Liseiwicz’s authentic letters have been withheld from the person they were meant to protect, while invented letters in that person’s name draw out the information he hopes to provide.

Affection, secrecy, and consequence

For nearly a year, Liseiwicz writes patiently without Rong Jinzhen receiving a single letter or knowing what is happening. The letters therefore do not persuade Jinzhen to return to Artificial intelligence, nor do they give him a chance to respond to Liseiwicz’s warning. The Party regards him instead as bait. His continued distraction with novels and chess does not prevent officials from exploiting the correspondence; they leave him alone because they believe they can use the relationship without his knowledge.

The episode establishes both the force and the vulnerability of Liseiwicz’s attachment to his former student. His letters combine practical warning with personal regret: he fears that Jinzhen has been drawn into the same kind of work that damaged his own life. Yet the very intimacy that gives the warning its urgency makes it useful to the surveillance apparatus. In this exchange, affection survives as a real motive, but it cannot control where a letter goes, who is allowed to read it, or whose voice its recipient believes he is hearing.