ASCII armor is a binary-to-textual encoding converter. ASCII armor is a feature of a type of encryption called pretty good privacy (PGP). ASCII armor involves encasing encrypted messaging in ASCII so that they can be sent in a standard messaging format such as email.
Techopedia explains ASCII-Armor
The reasoning behind ASCII armor for PGP is that the original PGP format is binary, which is not considered very readable by some of the most common messaging formats. Making the file into American Standard Code for Information Interchange (ASCII) format converts the binary to a printable character representation. Handling file volume can be accomplished through compressing the file.
Although ASCII armoring is a functional part of PGP, some developers and others worry about the potential for hacking in this system. A primary concern is often called ASCII armor parser vulnerability, and is related to the idea that a cleverly constructed ASCII armored detached signature file could be used as a kind of Trojan horse to introduce a replacement .dll that could activate a virus. This is seen as one of the major holes in an otherwise very effective encryption method.