Python Subprocess, how can I pass raw hex data to command line?

Question

I have a command cat hash.bin | openssl pkeyutl -sign -inkey privk.pem which can get result correctly.

Now I want to do it with python subprocess, I do it like this (where hash is read from hash.bin)

cmd = ['openssl', 'pkeyutl', '-sign', '-inkey ', prvk]
p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=STDOUT)
out = p.communicate(input=hash)[0]
print(out)

But openssl failed.

I can't use -in and -out because my code can't access to hard drive..

Which Python version are you using? Did you open `hash.bin` in binary mode? How did you read it if your code can't access the hard drive? — PM 2Ring, Mar 16 '16 at 10:24
@demonguy: really? So the trailing space had nothing to do with it? — mhawke, Mar 16 '16 at 22:34
Possible duplicate of [How can I process command line arguments in Python?](http://stackoverflow.com/q/567879) — jww, Mar 16 '16 at 22:42
unrelated: you could use `stdin=open('hash.bin', 'rb', 0)`, to emulate `cat hash.bin`. — jfs, Mar 18 '16 at 12:59

mhawke · Accepted Answer · 2016-03-16T11:56:12.180

1

The problem is caused by the stray space character following the inkey command.

Try removing the space and it should work:

cmd = ['openssl', 'pkeyutl', '-sign', '-inkey', prvk]

The reason is that Popen() is passing through the space character as part of the -inkey option's token. openssl is deciding that there is not an option named -inkey (with a space), so it exits. It is as if you were executing this from the command line:

cat hash.bin | openssl pkeyutl -sign '-inkey ' privk.pem

which fails.

edited Mar 16 '16 at 11:56

answered Mar 16 '16 at 10:34

mhawke

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@demonguy: I was wrong about that... getting tired. Answer updated. – mhawke Mar 16 '16 at 11:56
Thanks. It's indeed a trailing space after `inkey`, Thank you – demonguy Mar 17 '16 at 01:20

Python Subprocess, how can I pass raw hex data to command line?

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