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RSA Decrypt

Runs in browser

Decrypt RSA-OAEP ciphertext with your PEM private key in the browser. Supports RSA-2048 and RSA-4096. Private key never transmitted.

Last updated 02 Apr 2026

Paste Base64 RSA ciphertext and your PKCS#8 PEM private key, then click Decrypt to recover the original plaintext. Supports RSA-OAEP with SHA-256, SHA-384, and SHA-512. Fully browser-based via WebCrypto — your private key is never uploaded.

Note: RSA can only encrypt small amounts of data (up to ~200 bytes for RSA-2048). For large data, use AES and encrypt the AES key with RSA.

Never share your private key.

Key Pair

For large data encryption, use the AES Encrypt tool instead.
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How to use

  1. 1

    Generate or provide your private key

    Click 'Generate Key Pair' to create a new RSA-2048 or RSA-4096 key pair on this page, or paste your existing PKCS#8 PEM private key (begins with -----BEGIN PRIVATE KEY-----).

  2. 2

    Select Decrypt mode

    Click the 'Decrypt' tab in the mode toggle.

  3. 3

    Select the hash algorithm

    Choose the same hash algorithm used during encryption (SHA-256 by default). Mismatching the hash algorithm causes decryption to fail.

  4. 4

    Paste the Base64 ciphertext

    Paste the Base64-encoded RSA ciphertext into the input panel.

  5. 5

    Click Decrypt

    Click Decrypt. The plaintext appears if the private key matches the public key used for encryption.

  6. 6

    Copy the result

    Click Copy to copy the decrypted plaintext to your clipboard.

Frequently asked questions

What do I need to decrypt RSA ciphertext?
You need the Base64-encoded RSA ciphertext, the RSA private key in PKCS#8 PEM format corresponding to the public key used for encryption, and the hash algorithm selected during encryption (SHA-256 by default).
Is this tool safe? Is my private key sent to a server?
No. The private key never leaves your browser. Decryption uses the WebCrypto API, which runs entirely locally. No data is transmitted or logged. That said, treat your private key with care — never share it and store it in a secure location.
Are inputs sent to a server?
No. All RSA decryption is performed by the browser's native WebCrypto API. There are zero network requests during decryption.
Why does RSA decryption fail?
Common causes: wrong private key (the public/private key pair does not match), wrong hash algorithm selected (e.g. SHA-384 vs SHA-256), corrupted or truncated Base64 ciphertext, or the ciphertext was produced with a different RSA padding scheme (PKCS#1 v1.5 instead of OAEP).
What format does the private key need to be in?
PKCS#8 PEM format (the key begins with -----BEGIN PRIVATE KEY-----). Keys generated on this page are already in the correct format. OpenSSL-generated keys are typically PKCS#1 (-----BEGIN RSA PRIVATE KEY-----) and must be converted: openssl pkcs8 -topk8 -nocrypt -in key.pem -out key_pkcs8.pem
Can I decrypt OpenSSL RSA output here?
Yes, if the OpenSSL output was produced with RSA-OAEP padding and you have the PKCS#8 private key. Convert a PKCS#1 key to PKCS#8 first using: openssl pkcs8 -topk8 -nocrypt -in key.pem -out key_pkcs8.pem
What is the size limit for RSA decryption?
RSA-OAEP with SHA-256 and a 2048-bit key supports payloads up to 190 bytes of plaintext. RSA-4096 supports up to 446 bytes. For longer payloads, the ciphertext was likely produced with hybrid encryption — RSA-encrypted AES key plus AES-encrypted data.
What is RSA-OAEP?
RSA-OAEP (Optimal Asymmetric Encryption Padding) is the secure padding scheme for RSA encryption, standardized in PKCS#1 v2.2. It is far more secure than the older PKCS#1 v1.5 padding and is the only RSA encryption scheme supported by the WebCrypto API.
What is the difference between RSA-2048 and RSA-4096?
RSA-4096 provides a larger key (4096-bit modulus vs 2048-bit), making factoring harder. However, it is 4–8× slower for key generation and operations. RSA-2048 is considered secure through at least 2030. RSA-4096 provides extra margin at a performance cost.

Decrypt RSA-OAEP ciphertext using your private key directly in the browser.

All operations run on your device via the WebCrypto API — no data is

transmitted.

**RSA asymmetric decryption:** The public key encrypts; only the private key

can decrypt. This tool accepts Base64 ciphertext produced by the RSA Encrypt

tool on this site (RSA-OAEP scheme with SHA-256 by default).

**Getting started:**

1. Generate a key pair on this page (RSA-2048 or RSA-4096)

2. Paste the Base64-encoded RSA ciphertext

3. Paste your private key in PKCS#8 PEM format

4. Click Decrypt to recover the plaintext

**Important size limits:** RSA is designed for small payloads. The maximum

plaintext for RSA-2048 with SHA-256 is 190 bytes; RSA-4096 supports up to

446 bytes. For larger data, the standard workflow is hybrid encryption: the

sender encrypts a random AES key with RSA, then AES-encrypts the actual

payload. You decrypt the AES key with RSA, then decrypt the payload with AES.

**Privacy:** Your private key never leaves your browser. All decryption runs

via the WebCrypto API. Nothing is logged or transmitted.

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