This tool is for RSA encryption, decryption and to generate RSA key pairs online. Both public and private keys can be generated for free.
RSA (Rivest-Shamir-Adleman) is an asymmetric encryption
algorithm that uses two mathematically linked keys — a public key
to encrypt and a private key to decrypt. Because the keys are
different, RSA is widely used wherever two separate endpoints need to communicate
securely: VPN clients and servers, SSH connections, TLS handshakes, and digital
signatures.
Asymmetric Key Pair Public key encrypts; private key decrypts — keys are never the same
Multiple Padding Schemes OAEP (recommended), PKCS#1 v1.5, and RSA default
Flexible Key Sizes 512-bit to 4096-bit — generate a key pair directly in the tool
Generate RSA Key Pair
You can generate the required RSA public/Private keys here for encryption and
decryption.
Public Key(X.509 Format)
Private Key(PKCS8 Format)
RSA Encryption and Decryption
Below is the tool to perform RSA encryption and decryption. By default,
the
public/private keys are prepopulated with the keys generated above. You can also
supply
your own public/private key pairs.
RSA Encryption
RSA Decryption
Common RSA Encryption & Decryption Errors (and Fixes)
RSA Decryption Error: Bad Padding
This error occurs when the padding scheme used during encryption does not match
the padding used during decryption — for example, encrypting with
RSA-OAEP and attempting to decrypt with PKCS#1 v1.5.
See RSA Padding Schemes below for details.
Fix: Always use the same padding scheme for both encryption and decryption.
Ciphertext Too Large for RSA Key
RSA is not designed to encrypt large data or files directly. If the plaintext
exceeds the RSA key size limit (e.g. 2048 bits = 256 bytes minus padding overhead),
encryption will fail.
Fix: Use hybrid encryption — encrypt the data with AES, then encrypt the AES key using RSA.
Invalid or Unsupported RSA Key Format
RSA operations may fail if the private key is not in
PKCS#8
format or the public key is not in
X.509 format.
By default, this tool generates private keys in PKCS#8 and public keys in X.509 format.
Fix: Ensure private keys are PKCS#8 encoded and public keys are X.509 encoded. Validate your setup with our Crypto Safety Validator.
Key Features, Concepts & Security Considerations
Asymmetric Key Algorithm
Uses a mathematically linked public and private key pair. What one key encrypts, only the other can decrypt.
Security Basis
RSA security depends on the computational difficulty of factoring the product of two large prime numbers.
Variable Key Lengths
Supports 1024, 2048, 3072, and 4096-bit keys. A minimum of 2048 bits is recommended for production use.
Use Cases
Secure communication, digital signatures, TLS/SSL handshakes, and symmetric key exchange.
Public Key Structure
Composed of modulus n and public exponent e. Safe to share openly.
Private Key Structure
Uses private exponent d derived from Euler’s totient function. Must be kept secret and stored securely.
Secure Usage Guidelines for RSA
Use RSA only for key exchange or encrypting small secrets — not bulk data
Always prefer RSA-OAEP over PKCS#1 v1.5 for new implementations
Use a minimum key size of 2048 bits; prefer 4096-bit for long-lived keys
Never encrypt large files directly with RSA — use AES with RSA-wrapped key exchange instead
Private keys must be securely stored — never hardcode them in source code
Padding selection matters:
For secure RSA encryption, use
RSA/ECB/OAEPWithSHA-256AndMGF1Padding.
PKCS#1 v1.5 and SHA-1 based paddings are provided for legacy compatibility only and may cause decryption errors if mismatched.
When NOT to Use RSA Encryption
Large files: Use AES encryption instead — RSA has a strict per-operation size limit
Password storage: Use Argon2 or bcrypt — passwords must be hashed, not encrypted
Streaming or real-time data: Use ChaCha20 or AES-GCM for high-throughput scenarios
For a Java implementation of RSA encryption and decryption, follow
this article.
RSA Padding Schemes
PKCS#1 v1.5 — Legacy padding. Vulnerable to certain padding oracle attacks.
Explanation
OAEP (RSA/ECB/OAEPWithSHA-256AndMGF1Padding) — Recommended for all modern applications. Protects against chosen-ciphertext attacks.
Explanation
RSA is suitable for encrypting small secrets but not large files.
PGP encryption
combines RSA with symmetric encryption, making it far more practical
for file encryption.
Most failures are caused by a padding scheme mismatch, using the wrong key
(public instead of private or vice versa), or attempting to decrypt data
larger than the RSA key size allows.
No. RSA should only be used for encrypting small secrets or symmetric keys.
For files, use PGP or
AES-based encryption,
or try Devglan’s file encryption tool.
Use RSA/ECB/OAEPWithSHA-256AndMGF1Padding for all modern applications.
PKCS#1 v1.5 is only provided for legacy compatibility and is vulnerable to
padding oracle attacks.
A minimum of 2048 bits is recommended. 4096-bit provides a
meaningful increase in security for long-lived keys, though it comes with a
notable increase in CPU usage. 1024-bit and below are considered broken.
RSA is asymmetric (two different keys) and slow — designed for small data like key exchange.
AES is symmetric (same key) and fast — designed for encrypting bulk data.
In practice, RSA and AES are often combined: RSA encrypts the AES key, AES encrypts the data.
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signup-free.
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