About the Course

Cryptology: Math and Codes

  • Grades 5-7
  • CTY-Level
  • Individually Paced

Make and break secret codes in this exciting introductory cryptology course. You’ll begin with simple Caesar ciphers, learning to encrypt and decrypt messages as well as the history behind the cipher. We’ll then move through more advanced mathematical concepts to learn substitution ciphers, Vigenère ciphers, and multiplicative and affine ciphers. All of your newly acquired knowledge will be put to the test by finishing with public key cryptography and the modern-day RSA cryptosystem.

This course combines mathematics, computer science, and electrical engineering, and it’s an excellent choice for those wishing to enhance their grasp of modern cryptology concepts such as ATM cards, computer passwords, and e-commerce. Prepare to be challenged, though—many of the concepts covered in this course are often not seen until college. 

Your assigned CTY instructor will be available for learning support and one-on-one review sessions for graded assessments.

Recommended length of enrollment: 3 months

Group Session Meeting Times (optional): Mondays - 8 p.m. ET

Time Commitment: 5-8 hours per week (1 hour optional meeting, 5-7 hours independent work).

Students may enroll in this course at any time during the year.


Students enroll in a course by selecting an open class below. Students progress at their own pace following course guidelines, with guidance from instructors who strive to meet individual needs. While the course provides students with independence and flexibility, students must manage their time to complete the course before the end date.

Note: You need an active CTY Account to complete registration through MyCTY.

Up to 4.5 months of access
Choose your start date

Testing and Prerequisites

  Math Verbal
Required Level CTY-Level Not required
Check your eligibility using existing test scores If you do not have existing test scores:

Students must achieve qualifying scores on an advanced assessment to be eligible for CTY programs. If you don’t have qualifying scores, you have several different testing options. We’ll help you find the right option for your situation.

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Course Prerequisites

Cryptology: Math and Codes requires:

1 prerequisite

Successful completion of Grade 4 Mathematics or equivalent

Cost and Financial Aid

  • Tuition
    • Varies
  • Application fee
    • Nonrefundable Application Fee - $15 (Waived for financial aid applicants)
    • Nonrefundable International Fee - $20 (outside US only)

Financial Aid is available

We are committed to serving all talented youth regardless of financial circumstances. Financial assistance is available based on need.

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Course Materials

Please acquire all course materials by the course start date. If you have questions about these materials or difficulty locating them, please contact ctyinfo@jhu.edu.

Book Title: The Cryptoclub: Using Mathematics to Make and Break Secret Codes
Authors: Janet Beissinger and Vera Pless
ISBN: 978-156881-223-6

Technical Requirements

This course requires a computer with high-speed Internet access and an up-to-date web browser such as Chrome or Firefox. You must be able to communicate with the instructor via email. Visit the Technical Requirements and Support page for more details.

This course uses a virtual classroom for instructor-student communication. The classroom works on standard computers with the Zoom desktop client, and on tablets or handhelds that support the Zoom Mobile app. Recorded meetings can only be viewed on a computer with the Zoom desktop client installed. The Zoom desktop client and Zoom Mobile App are both free to download.

Terms & Conditions

You may have the option to post your work on public third-party sites (e.g., YouTube). 

Virtual class meetings may be recorded for students to review.

About Mathematics at CTY

Our online Mathematics courses—spanning elementary through college-level curricula—cover a wide range of topics, from algebra and geometry to chess, cryptology, and AP Calculus and are guided by expert instructors. You’ll join group sessions with classmates to ensure you stay on track with challenging course content. Whether you’re looking for pure math fun and enrichment, to move up the math ladder and advance your honors and AP (and beyond) academic standing, or to train for mathematics competitions, there’s a CTY course that’s right for you.

New math enrichment courses available!

Explore our new math enrichment courses, including Excursions in Pre-algebra, Mathematical Modeling, and Introduction to Logic and Proofs.

Meet our Mathematics Instructors