# RSA Encrypt / Decrypt Encrypt text with an RSA public key or decrypt ciphertext with the matching private key, using OAEP padding (SHA-1 or SHA-256). Handles long messages by chunking. Keys and data stay local. PKCS#1 v1.5 is intentionally not offered (Node disables it for decryption due to Bleichenbacher attacks). > Canonical page: https://elysiatools.com/en/tools/rsa-encrypt-decrypt - **Category:** Security - **Keywords:** rsa, encrypt, decrypt, oaep, pkcs1, asymmetric, cryptography, public key, private key, cipher ## Overview A practical RSA OAEP encryption/decryption tool. - **Mode**: encrypt (public key → ciphertext) or decrypt (private key → plaintext). - **Padding**: **OAEP** (Optimal Asymmetric Encryption Padding) with SHA-1 or SHA-256 hash. OAEP is the modern, semantically-secure scheme recommended for new RSA encryption. PKCS#1 v1.5 is intentionally omitted — it is vulnerable to Bleichenbacher padding-oracle attacks and Node.js refuses to decrypt with it. - **Chunking**: RSA can only encrypt a small block at once (key bytes − 2×hash size − 2). Messages longer than that are split into blocks, each encrypted separately, and the ciphertexts concatenated. Decryption splits on the modulus boundary and reverses it. - **Encoding**: ciphertext is hex or base64. Why OAEP max block = k − 2hLen − 2: OAEP adds a hash-length seed and label hash plus 2 delimiter bytes, so the usable payload per block shrinks accordingly. Use cases: end-to-end message encryption demos, encrypting a small payload to someone's public key, learning RSA in practice. Everything runs locally. ## Inputs - **Mode** (select) - **Public key (PEM)** (textarea): -----BEGIN PUBLIC KEY----- ... -----END PUBLIC KEY----- - **Private key (PEM)** (textarea): -----BEGIN PRIVATE KEY----- ... -----END PRIVATE KEY----- - **Private key passphrase (if encrypted)** (text): Only if the private key is passphrase-protected… - **Message (plaintext)** (textarea): The text to encrypt… - **Ciphertext (hex or base64)** (textarea): Paste the ciphertext produced by this tool… - **OAEP hash** (select) - **Ciphertext encoding** (select) ## When to use - When you need to encrypt a sensitive configuration value or API key using a recipient's RSA public key before sharing it. - When you need to decrypt a ciphertext payload locally using your passphrase-protected or unencrypted RSA private key. - When testing asymmetric encryption workflows or verifying RSA key pairs using secure OAEP padding configurations. ## How it works - Select the operation mode (encrypt with public key or decrypt with private key) and paste your PEM-formatted RSA key. - Choose the OAEP hash algorithm (SHA-256 or SHA-1) and the preferred ciphertext encoding format (Hex or Base64). - Input your plaintext message or ciphertext; the tool automatically chunks data exceeding the RSA block limit and processes it locally. ## Use cases - Encrypting database credentials with a production public key before committing them to a repository. - Decrypting automated alert payloads sent by external systems that encrypt data using your public key. - Verifying that a generated RSA public/private key pair functions correctly with OAEP padding. ## Frequently asked questions ### Why is PKCS#1 v1.5 padding not supported? PKCS#1 v1.5 is vulnerable to Bleichenbacher padding-oracle attacks and is disabled for decryption in modern runtimes like Node.js. ### How does the tool handle messages that exceed the RSA block size limit? It automatically splits the message into smaller chunks, encrypts or decrypts each block separately, and concatenates the results. ### Are my private keys or messages uploaded to a server? No. All encryption and decryption operations are performed locally in your browser, ensuring your keys and data never leave your device. ### What is the maximum payload size for a single RSA block? The maximum size is determined by the key size in bytes minus two times the hash length minus two (k - 2hLen - 2). ### Can I decrypt a private key that is protected by a passphrase? 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