Chaocipher is a method of encryption invented by John F. Byrne in 1918. For over 40 years, he unsuccessfully tried to interest various U.S. Government agencies and private industries in his cipher ...system. His 1953 biography included a series of challenge ciphers he labeled Exhibits 1-4. In 1990, John Byrne (son of John F. Byrne) revealed and demonstrated the Chaocipher algorithm to Professor Cipher Deavours and Louis Kruh. Without revealing the encipherment process, they in turn published an article including a new series of challenge ciphers they called Exhibit 5. Twenty-three years later, and three years after the first public revelation of the Chaocipher algorithm, Exhibit 5 remained unsolved. Following a 2013 visit to the National Cryptologic Museum (NCM) in Ft. Meade, Maryland to research the recently donated Byrne family materials on the Chaocipher, co-author Jeff Calof found two documents prepared by Deavours and Kruh pertaining to Exhibit 5. One document provides their encipherment schema and solution for the published version, while the other is for an earlier draft whose challenge ciphers differ markedly from that of the published article.
This article presents a review of Exhibit 5's creation, an analysis of the restrictions placed on Deavours and Kruh when writing their article, their enciphering schema and source material for the published Exhibit 5, irregularities with the published ciphertext, and an overview and comparison with their unpublished Exhibit 5 draft and challenge ciphers.
Transgenic expression of bacterial nitroreductase (NTR) enzymes sensitizes eukaryotic cells to prodrugs such as metronidazole (MTZ), enabling selective cell-ablation paradigms that have expanded ...studies of cell function and regeneration in vertebrates. However, first-generation NTRs required confoundingly toxic prodrug treatments to achieve effective cell ablation, and some cell types have proven resistant. Here we used rational engineering and cross-species screening to develop an NTR variant, NTR 2.0, which exhibits ~100-fold improvement in MTZ-mediated cell-specific ablation efficacy, eliminating the need for near-toxic prodrug treatment regimens. NTR 2.0 therefore enables sustained cell-loss paradigms and ablation of previously resistant cell types. These properties permit enhanced interrogations of cell function, extended challenges to the regenerative capacities of discrete stem cell niches, and novel modeling of chronic degenerative diseases. Accordingly, we have created a series of bipartite transgenic reporter/effector resources to facilitate dissemination of NTR 2.0 to the research community.
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