402 • ONE-TIME PADS
According to a report written by his Soviet contact, Dmitri Bystroly-
otov, he was given responsibility for the education of Oldham’s son,
who had been entrusted to the care of a German family living in a
villa on the Rhine near Bonn. This apparently gave Oldham a pretext
for traveling abroad and allowed him to deliver packets of documents
at frequent intervals. Not all the meetings took place in Germany;
some were held in Madrid, Ostend, and a resort in Switzerland.
After treatment for alcoholism, Oldham continued to drink and
beat his wife. In May 1933 he traveled to Paris and delivered another
batch of Foreign Office documents to Bystrolyotov, claiming that he
had no idea of precisely what the sealed package contained, but in-
sisting that he had paid his source for the contents in full. At this
meeting Oldham explained that he had offered to buy the Foreign
Office codebook known as ‘‘Book C’’ from his source, as well as
three cipher charts, for about three times the amount he had paid for
similar material a year earlier. In reality Oldham was working alone,
and he went undetected until he was named byWalter Krivitskyin
February 1940.ONE-TIME PADS (OTP).A supposedly secure system of enciphering
secret messages, an OTP depends on the two correspondents enci-
phering a text using an unique sequence of randomly generated num-
bers that are discarded once used, thus ensuring there is no repetition
or opportunity for a cryptographer to discern and exploit a pattern.
GCHQcryptanalysts discovered during World War II that the OTPs
in use by the German Foreign Ministry were susceptible to attack
because the five-figure numbers had been machine-generated and
therefore were not strictly random. The resulting traffic, known as
floradora, was distributed on a very limited circulation to author-
ized recipients in Whitehall.
GCHQ capitalized on this work when studying thevenonatraffic,
which had been enciphered by Soviet personnel using OTPs in which
some of the individual pages had been duplicated. Because GCHQ
had access to some of the original plain text and the encrypted mes-
sages that had been used for communicating lengthy bills of lading
for cargoes exported to the Soviet Union from the United States dur-
ing World War II, some of the duplicated traffic could be read. The
result was 2,900 messages either partially or completely solved cov-