History20th century (1943-1945)United States/Soviet Unionhigh confidence

American cryptologists needed almost two years to break the KGB's encryption used in VENONA-related communications.

Notes on verification

Confirmed by NSA's own official historical publication 'The Venona Story', corroborated by independent academic sources and NSA Cryptologic Foundation records, all consistent on the roughly two-year timeline. [tier=silver indep_score=0.875 clusters=2 claim_tier=notable]

Sources