We do not store or log any key you enter.
This tool is intended for personal and educational use.
Do not use online tools to protect real production secrets.
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 encryption and decryption.
Ciphertext Too Large for RSA Key
RSA is not designed to encrypt large data or files directly. If the plaintext size exceeds
the RSA key limit, encryption or decryption will fail.
Fix: Use hybrid encryption — encrypt the data using
AES, and 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.
Fix: Ensure private keys are PKCS#8 encoded and public keys are
X.509 encoded.
You can validate your setup using our
Crypto Safety Validator.
Secure Usage Guidelines for RSA
- Use RSA only for key exchange or small secrets
- Prefer RSA-OAEP over PKCS#1 v1.5
- Use a minimum key size of 2048 bits
- Never encrypt large files directly with RSA
Padding selection matters:
For secure RSA encryption, use
RSA/ECB/OAEPWithSHA-256AndMGF1Padding.
PKCS#1 v1.5 and SHA-1 based paddings are provided only for legacy compatibility
and may cause decryption errors if mismatched.
When NOT to Use RSA Encryption
For Java implementation of RSA, you can follow
this article
.
By default, the private key is generated in
PKCS#8
format and the public key is generated in
X.509 format
.
Key Features of RSA
- Asymmetric Key Algorithm: Uses a public and private key pair
- Security Basis: Depends on the difficulty of factoring large primes
- Variable Key Lengths: 1024, 2048, and 4096 bits
- Use Cases: Secure communication, digital signatures, key exchange
Key Concepts
-
Public Key: Composed of modulus n and exponent e
-
Private Key: Uses exponent d derived from Euler’s totient
function
Security Considerations
- Key Size: Larger keys provide stronger security
- Padding: Correct padding prevents cryptographic attacks
- Key Management: Private keys must be securely stored
RSA Padding Schemes
OAEP is recommended for modern applications as it protects against
chosen-ciphertext attacks.
RSA Encryption Through OpenSSL
Generate Private Key
$ openssl genrsa -out private.pem 2048
Export Public Key
$ openssl rsa -in private.pem -pubout -out public.pem
Encrypt Data
$ openssl rsautl -encrypt -inkey public.pem -pubin -in data.txt -out data.txt.enc
Decrypt Data
$ openssl rsautl -decrypt -inkey private.pem -in data.txt.enc -out data.txt
Applications of RSA
- SSL/TLS secure communication
- Digital signatures
- Secure symmetric key exchange
PGP vs RSA File Encryption
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.
| Feature |
PGP File Encryption |
RSA Encryption |
| Large file support |
Yes |
No |
| Multiple recipients |
Yes |
No |
| Hybrid encryption |
Yes |
No |
| Recommended for file sharing |
Yes |
Limited |
Frequently Asked Questions
Why does RSA decryption fail?
Most failures are caused by padding mismatch, incorrect key usage,
or attempting to decrypt data larger than the key size allows.
Is RSA safe for file encryption?
No. RSA should only be used for encrypting small secrets or keys.
For files, use PGP or AES-based encryption or try Devglan's file encryption tool.
Which RSA padding scheme should I use?
RSA-OAEP is recommended for modern secure applications.
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