Dr Shinobu Ishihara introduced in 1917 the most well known color blindness test. Each of his tests consists of a set of colored dotted plates, showing either a number or a path. Since then this is the most widely used color vision deficiency test and still used by most optometrists and ophthalmologists.
Public-key cryptography refers to a cryptographic system requiring two separate keys, one of which is secret and one of which is public. Although different, the two parts of the key pair are mathematically linked. One key locks or encrypts the plaintext, and the other unlocks or decrypts the ciphertext. Neither key can perform both functions by itself.