Machine learning by large could be used for Cryptanalysis. To identify patterns in Ciphertext and examine this under various settings of Ciphertext Indistinguishability
There are other techniques like "Learning with Errors" too for construction of Ciphers.
Trying to find patterns as a general approach in cryptography can be misleading even though it is part of a cryptanalytic process. Nothing is worthless in trying when it comes to cryptography, so it depends on where in terms of which domain you intended to engage it and how you wanted to do it. And machine learning approaches to cryptography may be possible and its strength cannot be predicted unless given a try.