非对称加密（das） 和 对称加密(des)文件
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声明：此文来源网络，本人按照原作者提供的方法做了一遍，是可行的。鉴于原文排版难于阅读，在这我重新排版，添加了个人部分自己的批注。
Linux关于文件加密的两种方法和详解：
- Linux关于文件加密的两种方法和详解：
- 一、用GnuPG加密文件。
- 1.第一步是要创建一个将来用来发送加密数据和进行解密数据的密钥。
- 2.为了把刚才生成的公共密钥发送给对方，我们需要先用命令把它提取出来：
- 3.在收到别人传过来的公共密钥后，需要把这个公共密钥放到“钥匙环”文件里：
- 4.接下来，我们在161机器上用201的公共密钥加密一个文件
- 5.最后我们把install.log.asc文件传回到201机器上，进行解密查看：
- 一、用GnuPG加密文件。
- 二、用openssl加密文件
-
- 1.加密一个文件：
- 2，解密文件
-
- 三、DSA算法
一、用GnuPG加密文件。
GnuPG软件包（Gnu Privacy Guard,Gnu隐私保镖）,软件包的名称是gpg。gpg在加密文件时使用的是公共密钥加密方法。1.第一步是要创建一个将来用来发送加密数据和进行解密数据的密钥。
我们执行一下gpg命令，就会在你的主目录下创建一个.gnupg子目录。（如果它不存在的话，有时已经存在了）。在该子目录里面有一个gpg.conf的配置文件，它里面是gpg工具的各种配置选项及其默认设置值。接下来，我们来进行第一项，生成密钥：
[root@fxvsystem root]# gpg --gen-key >>这个命令生成密钥
gpg (GnuPG) 1.2.4; Copyright (C) 2003 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.
Please select what kind of key you want: >>选择密钥类型
(1) DSA and ElGamal (default)
(2) DSA (sign only)
(4) RSA (sign only)
Your selection? 1
DSA keypair will have 1024 bits.
About to generate a new ELG-E keypair. >>选择密钥长度
minimum keysize is 768 bits
default keysize is 1024 bits
highest suggested keysize is 2048 bits
What keysize do you want? (1024) 768
Requested keysize is 768 bits
Please specify how long the key should be valid. >>选择密钥有效期，0代表没有期限
0 = key does not expire
<n> = key expires in n days
<n>w = key expires in n weeks
<n>m = key expires in n months
<n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct (y/n)? y >>最后确认是否正确
You need a User-ID to identify your key; the software constructs the user id
from Real Name, Comment and Email Address in this form:
"Heinrich Heine (Der Dichter) < [email protected]>"Real name: test201 >>输入基本信息，真实名字
Email address: [email protected] >>输入邮件地址
Comment: this is 201 key >>其他相关注释信息
You selected this USER-ID:
"test201 (this is 201 key) < [email protected]>"Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O >>确认OK
You need a Passphrase to protect your secret key.Enter passphrase: >>输入密钥口令
Repeat passphrase:We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
+++++.+++++++++++++++++++++++++++++++++++++++++++++.+++++..+++++++++++++++++++++++++++++++++++++++++++++.+++++..++++++++++.+++++++++++++++>.++++++++++...........................................................+++++
>>生成密钥过程会出现连续的这种符号。
Not enough random bytes available. Please do some other work to give
the OS a chance to collect more entropy! (Need 215 more bytes)
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy. >>这段话表明提示我们在系统上创建一些随机的活动，如果没有足够的活动，他会停下来提示我们继续这样做。（比如查看一下cpu,随意敲打一 下键盘都可以）
++++++++++.+++++++++++++++.++++++++++++++++++++.++++++++++.+++++++++++++++++++++++++.+++++.+++++.+++++++++++++++.+++++.++++++++++++++++++++....>+++++..+++++^^^^^
gpg: /root/.gnupg/trustdb.gpg: trustdb created
public and secret key created and signed.
key marked as ultimately trusted.pub 1024D/BA56DDDA 2007-01-16 test201 (this is 201 key) < [email protected]> 这行里面的BA56DDDA是生成的公共密钥的标识，我们在后面还要使用，记住它吧。
Key fingerprint = 98E8 0A56 9E16 F61B 379D 2F53 D5DF 4117 BA56 DDDA
sub 768g/8F754496 2007-01-16
>>成功
[root@fxvsystem root]#
[root@fxvsystem root]# cd .gnupg/
[root@fxvsystem .gnupg]# ll
total 24
-rw------- 1 root root 8075 Jan 16 11:10 gpg.conf
-rw------- 1 root root 856 Jan 16 11:30 pubring.gpg 存放别人公共密钥的“钥匙环”文件。
-rw------- 1 root root 0 Jan 16 11:10 pubring.gpg~
-rw------- 1 root root 600 Jan 16 11:30 random_seed
-rw------- 1 root root 991 Jan 16 11:30 secring.gpg
-rw------- 1 root root 1240 Jan 16 11:30 trustdb.gpg
[root@fxvsystem .gnupg]#
2.为了把刚才生成的公共密钥发送给对方，我们需要先用命令把它提取出来：
[root@fxvsystem gpg]# gpg --armor --export BA56DDDA > 201.key 把公共密钥提取到文件201.key中。其中：
--armor是让gpg生成ASCII格式的输出，这样适合电子邮件来发送。如果可以使用ssh等支持二进制文件传输的工具。可以不使用这个选项。
--export 就不用多说了，就是导出的意思。
3.在收到别人传过来的公共密钥后，需要把这个公共密钥放到“钥匙环”文件里：
比如，我们在另一台计算机上收到了刚才201.key这个公共密钥，然后我们执行：[root@localhost gpg]# gpg --import 201.key
gpg: key BA56DDDA: public key "test201 (this is 201 key) < [email protected]>" imported
gpg: Total number processed: 1
gpg: imported: 1
[root@localhost gpg]# gpg -kv
/root/.gnupg/pubring.gpg
------------------------
pub 1024D/1C05EC6B 2007-01-15
uid Paolo (this test destination 213) < [email protected]>
sub 1024g/A16A8685 2007-01-15
pub 1024D/BC3AA97D 2007-01-15
uid Wangqi (test to 161) < [email protected]>
sub 1024g/33A9764D 2007-01-15pub 1024D/BA56DDDA 2007-01-16
uid test201 (this is 201 key) < [email protected]>
sub 768g/8F754496 2007-01-16[root@localhost gpg]#
4.接下来，我们在161机器上用201的公共密钥加密一个文件
[root@localhost ~]# gpg -ea -r BA56DDDA install.log >>通过这个命令对install.log文件进行加密。
gpg: 8F754496: There is no assurance this key belongs to the named user
pub 768g/8F754496 2007-01-16 test201 (this is 201 key) < [email protected]>
Primary key fingerprint: 98E8 0A56 9E16 F61B 379D 2F53 D5DF 4117 BA56 DDDA
Subkey fingerprint: DC76 48E6 70C0 CD36 F671 D2D3 AEC5 02A2 8F75 4496It is NOT certain that the key belongs to the person named
in the user ID. If you *really* know what you are doing,
you may answer the next question with yes.Use this key anyway? (y/N) y
[root@localhost ~]# ls
-a 代表ASCII格式，如果不是通过电子邮件传输，可不加此参数
-r 后面是密钥的标识。可以使用多个-r参数，加多个标识，这样就可以把它发给多个需要该文件的人。
5.最后我们把install.log.asc文件传回到201机器上，进行解密查看：
[root@fxvsystem gpg]# ls
201.key install.log.asc
[root@fxvsystem gpg]# gpg -o install.log -d install.log.asc >>这个命令进行解密,-o为输出到一个文件中，-d表示解密。
You need a passphrase to unlock the secret key for
user: "test201 (this is 201 key) < [email protected]>"
768-bit ELG-E key, ID 8F754496, created 2007-01-16 (main key ID BA56DDDA)
gpg: encrypted with 768-bit ELG-E key, ID 8F754496, created 2007-01-16我们可以看到在当前目录下生成了一个install.log文件，这个文件就是解密后的文件，可以直接查看。
"test201 (this is 201 key) < [email protected]>"
[root@fxvsystem gpg]# ls
201.key install.log install.log.asc
[root@fxvsystem gpg]#
二、用openssl加密文件
openssl也可以进行文件的加密。方法比上面的gpg简单很多，没有创建密钥的过程，也没有相关的配置文件，只要执行一条命令就可以对文件进行加密。把加密的文件传给需要的人后，只要他知道加密方式和加密口令，就可以解密查看文件。
openssl支持的加密算法很多，包括：bf,cast,des,des3,idea,rc2,rc5等及以上各种的变体，具体可参阅相关文档。
1.加密一个文件：
[root@fxvsystem root]# openssl enc -des -e -a -in install.log -out install.log.des输入密码之后，就会生成install.log.des文件，这个文件名是自己指定的，可以随意写。
enter des-cbc encryption password:
Verifying - enter des-cbc encryption password:
其中：
enc表明你打算使用某个算法
-des是具体使用的某个算法
-e 表明要加密
-a 同样是使用ASCII进行编码
-in 要加密的文件名字
-out 加密后的文件名字
2，解密文件
把生成的文件传到另一台机器后，执行如下命令进行解密[root@fxvsystem gpg]# openssl enc -des -d -a -in install.log.des -out install.log
enter des-cbc decryption password:
其中
-d表明要进行解密
三、DSA算法
Digital Signature Algorithm (DSA)是Schnorr和ElGamal签名算法的变种，被美国NIST作为DSS(DigitalSignature Standard)。算法中应用了下述参数：
p：L bits长的素数。L是64的倍数，范围是512到1024；
q：p - 1的160bits的素因子；
g：g = h^((p-1)/q) mod p，h满足h < p - 1, h^((p-1)/q) mod p > 1；
x：x < q，x为私钥 ；
y：y = g^x mod p ，( p, q, g, y )为公钥；
H( x )：One-Way Hash函数。DSS中选用SHA( Secure Hash Algorithm )。
p, q, g可由一组用户共享，但在实际应用中，使用公共模数可能会带来一定的威胁。签名及验证协议如下：
1. P产生随机数k，k < q；
2. P计算 r = ( g^k mod p ) mod q
s = ( k^(-1) (H(m) + xr)) mod q
签名结果是( m, r, s )。
3. 验证时计算 w = s^(-1)mod q
u1 = ( H( m ) * w ) mod q
u2 = ( r * w ) mod q
v = (( g^u1 * y^u2 ) mod p ) mod q
若v = r，则认为签名有效。
DSA是基于整数有限域离散对数难题的，其安全性与RSA相比差不多。DSA的一个重要特点是两个素数公开，这
样，当使用别人的p和q时，即使不知道私钥，你也能确认它们是否是随机产生的，还是作了手脚。RSA算法却作不到。