如何Encrypt 大 Data

问题

你需要加密大 file 但 RSA 能够仅 加密少数 hundred bytes, 和你 want 安全的 公共-键加密.

前置条件

• Understanding 的 AES 和 RSA
• Knowledge 的 hybrid 加密

步骤

1. 1. Generate a random symmetric key

   Generate a fresh random AES key (256 bits). This key will encrypt the large data. It is called the session key or data encryption key (DEK). A new DEK should be generated for each file.

   输入

   random AES-256 key

   输出

   32 random bytes

2. 2. Encrypt the data with AES

   Encrypt the large file using AES-GCM with the session key and a fresh IV. AES can handle data of any size efficiently. Store the IV and authentication tag with the ciphertext.

   输入

   large file + AES key

   输出

   AES ciphertext + IV + tag

3. 3. Encrypt the session key with RSA

   Encrypt the small AES session key using the recipient's RSA public key with OAEP padding. Store the RSA-encrypted session key alongside the AES ciphertext. The recipient decrypts the session key with their private key, then decrypts the file with AES.

   输入

   AES key + RSA public key

   输出

   RSA-encrypted session key

预期结果

hybrid-encrypted 包: 大数据 encrypted 具有 AES, 和 AES 键 encrypted 具有 RSA, combining strengths 的两者.

常见错误

Trying to encrypt the large file directly with RSA

RSA can only encrypt data up to key_size - padding bytes. Use hybrid encryption for anything larger.

Reusing the AES session key across files

Generate a fresh session key for each encryption. Reusing it with the same IV breaks security.

排障指引

• If the RSA step fails with 'message too long', the session key exceeds the RSA limit. This should not happen with a 32-byte key and 2048+ bit RSA.
• Verify the GCM tag after AES decryption before using the data.

安全限制

• Hybrid encryption is the standard for TLS, PGP, and S/MIME. It provides public-key security with symmetric-key performance.
• All encryption is local; no keys or data are transmitted.