The following resources are available for practicing your Cryptography:
The following challenges were all taken from previous National Cyber League competitions starting in fall 2015 or are altered versions of challenges created for NCL competitions. All credit for these challenges is due to NCL and Cyber Skyline.
Because these challenges are the intellectual property of NCL and Cyber Skyline, I cannot release the answers to these challenges.
Selected challenges for practicing your Cryptography can be found here.