If you are interested in Cold War espionage...

....the NSA has a "Venona" site.

//Also, VENONA has excellent examples of the work of a KGB
agent and Communist Party functionary, covernames ECHO and
DICK (Bernard Schuster), in carrying out investigations on behalf of
the KGB as part of the vetting process of agent candidates (New York
to Moscow, Nos. 1221, 1457, and 1512, all from 1944).

Alger Hiss, a veteran GRU agent,
is presumably found in one KGB
message: Washington to Moscow,
no. 1822, 30 March 1945. In this
message, A, meaning the chief
Illegal ALBERT (Iskak Akhmerov)
reports about his interview of ALES,
who describes his recent GRU career
and says he has been a GRU agent
continuously since 1935. Analysts
later identified ALES as probably
Hiss. Presumably, ALBERT was
examining the possibility of
transferring Hiss from GRU to the
KGB.