Computer Cryptography Basic Knowledge 計算機密碼學基本知識

There are three basic types of encrypt/decrypt strategies.
Symmetric – use only one key, the secret key. Both encryption and decryption use this key. This method is fast but have key distribution problem. How do you share the key with people receiving cypher from you?
Asymmetric – Two keys involve the strategy, one public key and one private key. You spread your public key, people encrypt data with it and send the cypher back to you, you decrypt the cypher with private key. vice versa. This method is slower than symmetric one but without the key distribution problem.
Hybrid – Have the ablities of being both safe and fast by combining the above strategies. Solve the symmetric key distribution problem by encrypting the secret key with your given public key, send it back. The receiver will decrypt the secret key with his/hers private key. Then you get the speed of symmetric method by encrypting and decrypting data with secret key.

計算機理論裡有三種最基本的加密方法
對稱加密法 – 只用一把金鑰,叫秘密金鑰好了. 加密跟解密都使用這一把金鑰完成. 這個方法很快,但缺點是金鑰發佈問題. 你要怎樣安全地把金鑰送給密件收件人呢?
非對稱加密法 – 要用兩把金鑰, 一把公用金鑰和一把私有金鑰. 你把自己的公用金鑰發佈出去, 想傳資料給你的人用這金鑰加密並把密件回傳給你. 你用你的私有金鑰解密. 相反也用同樣做法. 這方法比對稱法慢但沒有金鑰發佈問題.
混合法 – 結合上面兩種方法使之既快速且安全的. 把秘密金鑰先用別人給你的公用金鑰先加密,發佈出去. 收件人再用其私有金鑰把秘密金鑰取出. 接著雙方就可以用同個秘密金鑰互送資料.

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