British Cypher No. 5We must not mix up 'British Cypher No. 5' with 'Naval Cypher No. 5'. Most historical references are to 'Naval Cypher No. 5'. This codebook is dated 25th June 1921 and was not used in WW2. Dr Thomas Cheetham who works at the Bletchley Park Trust has recently pointed out (18/11/2024) the following paragraph from a document in the National Archives: Paragraph 62 of the Royal Navy history named 'Security of Naval Codes and Cyphers' (National Archives file ADM 1/27186). '... Later, this disadvantage was largely overcome by use, in particularly hazardous operations, of a long-since obsolete four-figure book, "British Cypher No. 5", together with 2, 3, 6 or 20 way series of One-time Pads. This, of course, provided complete security in spite of the known compromise of the basic cypher.' It's worth noting that use of codebooks have the advantage of text compression. Due to the size of these files, (32kB typ, 78kB max) they have been split into 6 groups. All except for the cover were scanned in black and white to reduce bandwidth. However, due to ageing of the paper, editing and ink smudges, quality is not ideal. Obvious blemishes have been edited out. Front cover, title page and contents pages
Comments welcome: Keith |