This paper presents the design, implementation, and evaluation of a new framework called CryptoScratch, which extends the Scratch programming environment with modern cryptographic algorithms (e.g., AES, RSA, SHA-256) implemented as visual blocks. Using the simple interface of CryptoScratch, K-12 students can study how to use cryptographic algorithms for services like confidentiality, authentication, and integrity protection; and then use these blocks to build complex modern cryptographic schemes (e.g., Pretty Good Privacy, Digital Signatures). In addition, we present the design and implementation of a Task Block that provides students instruction on various cryptography problems and verifies that they have successfully completed the problem. The task block also generates feedback, nudging learners to implement more secure solutions for cryptographic problems. An initial usability study was performed with 16 middle-school students where students were taught basic cryptographic concepts and then asked to complete tasks using those concepts. Once students had knowledge of a variety of basic cryptographic algorithms, they were asked to use those algorithms to implement complex cryptographic schemes such as Pretty Good Privacy and Digital Signatures. Using the successful implementation of the cryptographic and task blocks in Scratch, the initial testing indicated that $\approx 60\%$ of the students could quickly grasp and implement complex cryptography concepts using CryptoScratch, while $\approx 90\%$ showed comfort with cryptography concepts and use-cases. Based on the positive results from the initial testing, a larger study of students is being developed to investigate the effectiveness across the socioeconomic spectrum.