What is Decryption?
The process of converting encrypted data (ciphertext) back into readable form (plaintext) using the correct key. Decryption is the inverse of encryption—only those with the proper key can decrypt.
Encryption is useless without decryption. The two are inseparable—you encrypt to protect, you decrypt to use.
How Decryption Works
- Symmetric: Same key that encrypted also decrypts (AES, ChaCha20)
- Asymmetric: Private key decrypts what was encrypted with the public key (RSA, ECC)
- Hybrid: Asymmetric decrypts a symmetric key, which then decrypts the data (TLS, PGP)
Who Can Decrypt
- You: With your private key or password
- Recipient: In E2EE messaging, only the intended recipient has the key
- Service provider: In encrypted-at-rest storage, they hold the keys—they can decrypt
- Attackers: If they obtain the key through theft, coercion, or weak crypto
Decryption and Privacy
- E2EE: Only endpoints can decrypt—not even the service provider
- Encrypted backup: You hold the only key—lose it, lose access
- Government access: "Going dark" debate—law enforcement wants decryption backdoors
- Key escrow: Storing keys with third parties—defeats purpose of encryption
Related Terms
Encryption
The process of converting information into a code to prevent unauthorized access. Encryption transforms readable data (plaintext) into an unreadable format (ciphertext) using a cryptographic algorithm and key. Only those with the correct key can decrypt and read the original data.
End-to-End Encryption
A method of secure communication where only the communicating users can read the messages. In principle, it prevents potential eavesdroppers – including telecom providers, Internet providers, and even the provider of the communication service – from being able to access the cryptographic keys needed to decrypt the conversation.
Public Key Cryptography
A cryptographic system that uses pairs of keys: public keys (which may be disseminated widely) and private keys (which are known only to the owner). This enables secure communication between parties who have never met and forms the basis for digital signatures, key exchange, and encrypted communication.
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