# Fundamentals of Encryption What is a digital signature? > A piece of encrypted data added to other data to verify the sender Which of the following uses key sizes equal to 128, 192 and 256 bits? > AES Blowfish is an asymmetric stream cipher > False Which hashing algorithm do modern Windows systems use? > NTLM Secure Multipurpose Internet Mail Extensions (S/MIME) use X.509 certificates to secure e-mail communication > True Which encryption algorithm uses a variable length symmetric key? > Blowfish Which of the following is a symmetric key system using blocks? > DES What is the purpose of a certificate? > To validate the sender of a digital signature or software Which of the following is an encryption method developed by three mathematicians? > RSA Which of the following encryption algorithms is a block cipher and uses the Rijndael algorithm? > AES --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://wiki.zacheller.dev/network-security/courses/isci-cnss-course/fundamentals-of-encryption.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.