加密檔案 - OpenSSL

Create Example Reference File, let us create a 1GB large text file using the fallocate command:

fallocate -l 1024M test.txt
echo "LinuxShellTips tutorial on encrypting a large file with OpenSSL in Linux" >> test.txt
cat test.txt

Encrypt File with Password (對稱式加密)

openssl enc -aes-256-cbc -pbkdf2 -p -in test.txt -out test.txt.enc

• enc executes the symmetric key encryption process.
• -aes-256-cbc specifies the use of 256 bits cryptographic key.
• -pbkdf2 is the default algorithm being used.
• -p prints used salt, key, and IV.
• -in points to the input file.
• -out points to the output file.

To decrypt the file, run:

openssl aes-256-cbc -d -pbkdf2 -in test.txt.enc -out sample_decrypted.txt

You will be required to enter the encryption password you generated earlier.

Encrypt File with Key (對稱式加密)

# generate a key file
openssl rand 256 > symmetric_keyfile.key
# use the keyfile to encrypt our file
openssl enc -in test.txt -out test.txt.enc -e -aes-256-cbc -pbkdf2 -k symmetric_keyfile.key

To decrypt the file, run:

openssl enc -in test.txt.enc -out draft_decrypted.txt -d -aes-256-cbc -pbkdf2 -k symmetric_keyfile.key

非對稱式加密 (Asymmetric Encryption)

使用非對稱式加密對一個大檔案進行加密，可能遇到錯誤: data too large for key size.

TIP: 非對稱加密又稱公鑰加密。在使用前要準備好一對私鑰與公鑰，使用公鑰進行檔案的加密，解密時則使用私鑰，操作上較複雜，但是安全性較佳。

Hashing

# For file
openssl dgst -sha256 my.file

# For string
echo "HelloWorld" | openssl sha256

參考網站

• OpenSSL 對稱式、非對稱式加密檔案指令教學與範例