Plaintext.

Plaintext is the original, human- or machine-readable representation of information before encryption is applied or after it has been correctly decrypted. In cryptographic protocols the term distinguishes data inside the trust boundary from ciphertext that may safely traverse hostile channels. It is also the classic axis of cryptanalysis: a known-plaintext attack exploits matched plaintext/ciphertext pairs, while a chosen-plaintext attack lets the adversary encrypt inputs of their choosing — the very threat that IND-CPA security and randomized/AEAD modes are designed to defeat.

In applied security, "stored in plaintext" is shorthand for a serious failure. The 2012 LinkedIn breach exposed 6.5 million unsalted SHA-1 password hashes (later revealed to cover ~117 million accounts), and RockYou's 2009 breach leaked 32 million passwords in outright plaintext — both fed the wordlists still used to crack accounts today. Adobe's 2013 breach compounded the problem by encrypting 150+ million passwords with ECB-mode 3DES and a shared key, so identical passwords produced identical ciphertext. Defensive practices: never store credentials as plaintext or reversible ciphertext — use a salted, memory-hard KDF (Argon2, bcrypt, scrypt); encrypt data at rest with strong AEAD ciphers (AES-GCM, ChaCha20-Poly1305); enforce TLS in transit; and redact plaintext secrets from logs, error messages, URLs and referrer headers.

flowchart LR
  A[Plaintext<br/>inside trust boundary] -->|encrypt with key| B[Ciphertext]
  B -->|hostile channel| C[Ciphertext]
  C -->|decrypt with key| D[Plaintext recovered]
  A -. leak: logs, plaintext store .-> E[Exposure]
  B -. weak cipher / no salt .-> E