RSA Encrypt, Decrypt, Sign & Verify
RSA in your browser: encrypt and decrypt with OAEP (SHA-256/SHA-1) or PKCS#1 v1.5, sign and verify with PKCS#1 v1.5 or PSS, using PEM or JWK keys.
RSA is the public-key algorithm behind TLS certificates, SSH keys and many signature schemes: anyone with the public key can encrypt or verify, and only the private key can decrypt or sign. This tool performs all four operations in your browser with PEM or JWK keys — OAEP or PKCS#1 v1.5 encryption, and PKCS#1 v1.5 or PSS signatures with SHA-256, SHA-384 or SHA-512 — and interoperates with OpenSSL.
How to use this tool
- Choose encrypt, decrypt, sign or verify.
- Paste the key: a public key for encrypt and verify, the private key for decrypt and sign (PEM or JWK).
- Pick the padding or signature scheme the other side uses.
- Paste the message (text, Base64 or hex) and, to verify, the signature; copy the Base64 or hex result.
Formula
c = mᵉ mod n (encrypt / verify) m = cᵈ mod n (decrypt / sign)
n is the modulus, e the public and d the private exponent; m is the padded message. OAEP padding (RFC 8017) is randomised and proven secure; PKCS#1 v1.5 encryption is legacy. A k-byte key encrypts at most k − 2·hLen − 2 bytes with OAEP (190 for 2048 bits with SHA-256) or k − 11 bytes with PKCS#1 v1.5. PSS uses a salt as long as the hash.
Example
With a 2048-bit key, "Hello RSA" encrypts to a 256-byte ciphertext (344 Base64 characters) that is different every time. OpenSSL’s openssl pkeyutl -encrypt -pkeyopt rsa_padding_mode:oaep -pkeyopt rsa_oaep_md:sha256 output decrypts here with "RSA-OAEP with SHA-256", and openssl dgst -sha256 -sign produces exactly the RS256 signature this page makes.
Frequently asked questions
Why is my decryption failing?
The padding must match exactly: OpenSSL’s plain -pkeyopt rsa_padding_mode:oaep uses SHA-1, Web Crypto and JOSE usually use SHA-256, and older tools use PKCS#1 v1.5. Also check that the ciphertext is Base64 or hex of exactly the key size.
Can I encrypt a whole file with RSA?
No — RSA can encrypt only a little less than the key size. Real systems encrypt the data with AES and use RSA to encrypt the AES key (hybrid encryption).
Is it safe to paste a private key here?
The key stays in the page: it is processed with the browser’s Web Crypto API, never uploaded, and the key box is never written into share links or history. Still, prefer test keys, and keep production keys in a key store.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/rsa-encrypt-tool/
Cite or embed this tool
kakaoCalc. (2026, November 8). RSA Encrypt, Decrypt, Sign & Verify. https://kakao.mobile/tools/rsa-encrypt-tool/
“RSA Encrypt, Decrypt, Sign & Verify.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/rsa-encrypt-tool/.
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