Walsingham’s cryptanalyst ran a double-agent ‘beer barrel’ letter trap, hosts say

What was said

"Gifford's approach to Mary had been a setup supervised by Phillips. And it's Phillips as well who had recruited the brewer. So basically, you know, he's holding all the strings. And he has been opening all the correspondence between Babington and Mary. He's been decrypting what Babington may have written or what Mary may have written, reading it through, and then he is another of his many talents is that he's able to reseal letters that he's opened and make it look as though they have never been opened."

Tom Holland describes an intelligence operation in which Elizabeth I’s spymaster Francis Walsingham allegedly ‘turned’ courier Gilbert Gifford and used cryptanalyst Thomas Phelippes to intercept Mary’s coded correspondence. Holland says Phelippes supervised a concealment method using beer barrels, decrypted the letters, and resealed them to avoid detection as the messages continued to their recipients.