The -k argument on my openssl accepts a passphrase, not a file. You likely encrypted with the filename as the secret, not it’s contents. Perhaps you should use -kfile instead.
<span style="color:#323232;">$ openssl aes-256-cbc -help
</span><span style="color:#323232;">Usage: aes-256-cbc [options]
</span><span style="color:#323232;">
</span><span style="color:#323232;">General options:
</span><span style="color:#323232;"> -help Display this summary
</span><span style="color:#323232;"> -list List ciphers
</span><span style="color:#323232;"> -ciphers Alias for -list
</span><span style="color:#323232;"> -e Encrypt
</span><span style="color:#323232;"> -d Decrypt
</span><span style="color:#323232;"> -p Print the iv/key
</span><span style="color:#323232;"> -P Print the iv/key and exit
</span><span style="color:#323232;"> -engine val Use engine, possibly a hardware device
</span><span style="color:#323232;">
</span><span style="color:#323232;">Input options:
</span><span style="color:#323232;"> -in infile Input file
</span><span style="color:#323232;">** -k val Passphrase**
</span><span style="color:#323232;"> -kfile infile Read passphrase from file
</span>