So it's not the most secure practice to pass a password in through a command line argument. That said, the documentation for openssl confused me on how to pass a password argument to the openssl command.

Here's what I'm trying to do

openssl aes-256-cbc -in some_file.enc -out some_file.unenc -d

This then prompts for the pass key for decryption. I searched the openssl documents and the interwebs to try and find the answer if I simply wanted to give the password to the command without trying to echo the password to the file. I tried adding -pass:somepassword and -pass somepassword both with and without quotes to no avail.

I finally figured out the answer and saw in some other forums people had similar questions, so I thought I would post my question and answer here for the community.

note: I'm using openssl version 0.9.8y


The documentation wasn't very clear to me, but it had the answer, the challenge was not being able to see an example.

Here's how to do it:

openssl aes-256-cbc -in some_file.enc -out some_file.unenc -d -pass pass:somepassword

Notice that the command line command syntax is always -pass followed by a space and then the type of passphrase you're providing, i.e. pass: for plain passphrase and then the actual passphrase after the colon with no space.

Additionally the documentation specifies you can provide other passphrase sources by doing the following:

  • env:somevar to get the password from an environment variable
  • file:somepathname to get the password from the first line of the file at location pathname
  • fd:number to get the password from the file descriptor number.
  • stdin to read from standard input

Now that I've written this question and answer, it all seems obvious. But it certainly took some time to figure out and I'd seen it take others similar time, so hopefully this can cut down that time and answer faster for others! :)

With OpenSSL 1.0.1e the parameter to use is -passin or -passout. So this example would be:

openssl aes-256-cbc -in some_file.enc -out some_file.unenc -d -passin pass:somepassword

  • 1
    What's the difference between using passin or passout? - Ha! Just looked it up, stdin vs stdout of course! – dtmland Jun 14 '17 at 22:29
  • Note that the documentation for password options applying to most openssl commands (not just enc) is in the man page for openssl(1) also on the web under 'OPTIONS'. But I don't believe your last bit about -passin/out; other openssl commands like rsa dsa ec pkey pkcs8 pkcs12 req ca do use those but in every version I've seen including 1.0.1e built directly from upstream source enc uses -pass or -k -kfile as documented (on the enc manpage). – dave_thompson_085 Jun 18 '17 at 11:52
  • 1
    How about the openssl dgst command? How do you enter the passphrase for that at the command line? – frakman1 May 11 '18 at 16:47
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    btw -passin is used to provide a password for the input certificate, and -passout is for the new generated certificate – drmad May 20 '18 at 2:44

I used -passin and -passout to set passwords to both files in example:

openssl pkcs12 -in voip.p12 -out voip.pem -passin pass:123 -passout pass:321

where 123 and 321 are password


At this moment Ubuntu 14.04 LTS comes with openssl 1.0.1f-1ubuntu2.16

In this version the parameter to use is -k


openssl enc -aes-256-cbc -e -in some_file.unenc -out some_file.enc -k somepassword
  • 2
    in your example, -k is an option available to the openssl 'enc' command (try man enc) it is not a general option. If you look at man openssl you'll see under the 'Pass Phrase Options' heading, what the general options are; pass:password, env:var, file:pathname, fd:number or stdin, as mentioned in an earlier response. – sibaz Aug 24 '17 at 10:55

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