The Kasiski examination is a cryptanalytic technique used to break the Vigenère cipher, which is a form of polyalphabetic substitution cipher. Key aspects include:

1. **Pattern Detection:** Identifies repeated sequences of ciphertext, which can reveal the length of the cipher's key.

2. **Distance Analysis:** Measures the distances between occurrences of the same ciphertext sequence. If the key is repeated, these distances will often be multiples of the key length.

3. **Key Length Calculation:** By analyzing these distances and their factors, cryptanalysts can estimate the length of the key used in the cipher.

4. **Frequency Analysis Application:** Once the key length is known, the ciphertext can be divided into segments corresponding to each position of the key, allowing for frequency analysis to break each segment as a simple substitution cipher.

The Kasiski examination is a fundamental technique in cryptanalysis for deciphering polyalphabetic ciphers and understanding the encryption structure.