In historical cryptography, a cipher key represents a set of rules by which we can convert between plaintext and ciphertext within an encryption system. Presently, there are not many studies that focus on analysing keys,especially not on a large scale or done in a systematic manner. In this paper, we describe a uniform transcription standard for the keys in the DECODE database. This way, we intend to lay a strong foundation to facilitate further studies on large sets of key transcriptions. We believe that a homogeneous set of transcriptions would be an ideal starting point for comparative studies, especially from a chronological perspective, as this can reveal potential patterns in the evolution of encryption methods. We also build a script that can perform an in-depth analysis of the components of a key, using our standardized transcription files as input. Finally, we give a detailed account of our findings and show that our method can reliably extract valuable information from the transcription file, such as the method of encryption or the types of symbols used for encoding, without the need of additional manual analysis of the original key.