How decryption works
In symmetric encryption, the same secret key that encrypted the data is used to decrypt it. In asymmetric encryption, data encrypted with a public key is decrypted with the matching private key, so the secret never has to be shared in advance.
Software handles this automatically in most cases, such as when a browser decrypts a TLS session or a laptop decrypts its disk at login. The security of the process rests on protecting the decryption keys. If an attacker obtains the key, they can read everything protected by it.
Why it matters for Canadian organizations
Encrypted data is only useful if authorized people can still decrypt it, so lost or poorly managed keys can mean permanent loss of important records. Availability and integrity of information are part of a sound safeguard under PIPEDA and Law 25.
Decryption also has a security-monitoring side. Many threats hide inside encrypted traffic, so some organizations inspect TLS traffic at the network edge, which must be done carefully with privacy and legal considerations in mind. Ransomware victims face a related question about decryption keys, and paying offers no guarantee of recovery.
How to implement it
Control who and what can decrypt sensitive data. Store keys in a hardware security module or managed key service, separate them from the data they protect, and restrict access using least privilege and logging.
Plan for recovery by backing up keys securely and testing that encrypted backups can be restored. Where TLS inspection is used, limit it to appropriate traffic and document it in privacy impact assessments. Rotate keys on a schedule and when staff with access leave. Test decryption in recovery drills, not only during live incidents.
Frequently asked questions
What is the difference between encryption and decryption?
Encryption scrambles readable data into ciphertext to protect it, while decryption reverses the process to restore the original data. Both rely on algorithms and keys, and each is meaningless without the other. Without the right key, neither can be undone, so key custody is critical.
Can encrypted data be decrypted without the key?
Not in practice with strong modern algorithms and sufficiently long keys. Attackers instead target weak passwords, stolen keys, or implementation flaws. This is why key protection is so important. Never rely on attackers to provide a working key after paying a ransom.
Can ransomware-encrypted files always be decrypted?
No. Without the attacker's key, recovery is often impossible, though free decryptors exist for some older ransomware families. The most dependable recovery path is restoring from clean, tested backups. Report the incident to the Canadian Centre for Cyber Security and consult responders.
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