Symmetric Encryption: Same Key Used to Encrypt and Decrypt?

SY0-701 By islever Editorial Last updated

Explain the importance of using appropriate cryptographic solutions.

Short answer

A Symmetric encryption uses one shared key to both encrypt and decrypt the message between the administrator and the branch-office peer.

Question

A systems administrator uses a key to encrypt a message being sent to a peer in a different branch office. The peer then uses the same key to decrypt the message. Which of the following describes this example?
  1. Symmetric Correct Answer
  2. Asymmetric
  3. Hashing
  4. Salting

Key Takeaways

The exam tests whether you can identify a cryptosystem from the key relationship — one shared key for both directions means symmetric — while the trap is confusing it with asymmetric encryption, which uses a mathematically related key pair instead.

When one systems administrator encrypts a message with a key that a peer in another branch office uses to decrypt it, the shared single key makes this symmetric encryption. This page confirms why the SY0-701 answer is Symmetric rather than asymmetric, hashing, or salting, and how the exam words that distinction.

Common mistake: Some candidates pick Hashing or Salting because both involve cryptographic operations on the message, but neither is reversible encryption: hashing is one-way and salting adds random data before hashing, so a peer could never decrypt an original message from either.

Expert Analysis

Why the Answer Is Correct

Symmetric encryption is defined by a single secret key that performs both the encryption and decryption transformations — here the administrator encrypts the branch-office message and the peer decrypts it with that identical key. The scenario gives no public/private key pair, no certificate exchange, and no key-derivation step, so nothing suggests anything other than a shared secret cipher such as AES. This is also the fastest and most common way to protect bulk data in transit, which matches the described administrative use case. Because the question hinges purely on "the same key" being used on both ends, Symmetric (A) is the only option that describes the operation accurately, and the community reference to "the same key for both processes" captures exactly that logic.

Why the Other Options Are Wrong

Asymmetric encryption (B) uses two mathematically related keys — a public key to encrypt and a private key to decrypt — so the peer would not be using the administrator's exact same key. Hashing (C) is a one-way integrity function that produces a fixed-length digest and cannot be reversed, so a recipient could never recover the original message from it. Salting (D) is a technique for defeating precomputed rainbow-table attacks by appending random data before hashing a password, and it has nothing to do with encrypting a message between two offices. None of these three options supports the stated "same key" decryption requirement.

Community Comment Notes

Consensus among commenters is strong for the symmetric interpretation: Dlover states "Symmetric same key to encrypt and decrypt" and 123456789User likewise notes that the same key used to encrypt is used to decrypt. MAKOhunter33333333 reinforces the point simply as "The same key for both processes," and nesquick0, c80f5c5 and Shaman73 all land on A. Interestingly, shady23 selected option C in the vote record but described symmetric encryption in the text, which is a useful reminder that mis-clicking — not misunderstanding — often explains stray votes in these polls.

Official Reference

https://csrc.nist.gov/glossary/term/symmetric_key

This link opens the official vendor documentation in a new tab.

Exam Strategy

When a crypto scenario mentions keys, first count them: one key shared by both parties is symmetric, while two related keys (public/private) are asymmetric. Then immediately scan the remaining options for reverse-engineering traps such as hashing or salting, which are one-way and can never recover a plaintext message.

Frequently Asked Questions

Why isn't asymmetric encryption the answer if a key is used to communicate between two offices?

Asymmetric encryption requires a key pair, not one shared key — the sender encrypts with a public key and the receiver decrypts with the matching private key, which the question never describes.

Why can't hashing or salting decrypt the branch-office message?

Hashing is a one-way integrity function and salting just adds random data before hashing, so neither produces a reversible ciphertext that the peer could decrypt back into the original message.

More SY0-701 FAQ →

Community Votes

A
85%
C
15%

85% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. Dlove 👍 5 Answered A
    A. Symmetric same key to encrypt and decrypt
  2. MAKOhunter33333333 👍 5 Answered A
    The same key for both processes
  3. shady23 👍 4 Answered C
    Symmetric Encryption In this type of encryption, there is only one key, and all parties involved use the same key to encrypt and decrypt information.
  4. 123456789User 👍 4 Answered A
    Symmetric: Same key is used to encrypt as is used to decrypt.
  5. nesquick0 👍 4 Answered A
    A. Symmetric
Show 1 more comment
  1. c80f5c5 👍 4 Answered A
    symmetric

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