**A: **This depends on if you want symmetric or asymmetric encryption.

For symmetic encryption, you can use the following…

To encrypt:

> openssl aes-256-cbc -salt -a -e -in plaintext.txt -out encrypted.txt

To decrypt this, you can use the following.

> openssl aes-256-cbc -salt -a -d -in encrypted.txt -out plaintext.txt

Now, for Asymmetric encryption you must first generate your private key and extract the public key.

> openssl genrsa -des3 -out private.key 4096 > openssl -in private.key -pubout -out public.key

To encrypt:

> openssl rsautl -encrypt -pubin -inkey public.key -in plaintext.txt -out encrypted.txt

To decrypt:

> openssl rsautl -decrypt -inkey private.key -in encrypted.txt -out plaintext.txt

Get more on OpenSSL here.

http://gaurang17.blogspot.in/2013/03/using-openssl.html

It is hard to see the whole command-line and it requires scrolling ;(

Please make it go away!

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Unfortunately, the rsautl command lines only work for very small files. For larger files I get this error:

4052:error:0406D06E:rsa routines:RSA_padding_add_PKCS1_type_2:data too large for key size:rsa_pk1.c:151

See http://blog.altudov.com/2010/09/27/using-openssl-for-asymmetric-encryption-of-backups/ for an alternative.

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