In the material's OpenSSL signing command, the sender uses `private.pem` and the `-sign` option to create a signature file named `document.sha256` from `document.txt`. The key used to create that signature is the sender's _____ key.

### Why this is right The example command explicitly supplies `private.pem` after the `-sign` option, so the signing key is the sender’s private key. The corresponding public key is used later by the recipient for verification. ### The concept The signing command in the material is `openssl dgst -sha256 -sign private.pem -out document.sha256 document.txt`. It calculates a hash of `document.txt` using the named algorithm and uses the private key to create the signature output file. The recipient checks that output against the document using the public key. The file extension and filename are labels for the files; the important roles are the private key for signing, the signature file as verification input, and the public key for verification. A signature does not encrypt the original text file. ### Terms - **OpenSSL**: software that provides cryptographic tools, including the command-line utility shown. - **SHA-256**: Secure Hash Algorithm 256, the hash algorithm specified in the command. - **Hash**: a compact value calculated from data and used in the signing process. - **Private key**: the key used here to create the signature. - **Public key**: the corresponding key used to verify the signature. - **Signature file**: the file containing the cryptographic signature output. ### Remember In the example command, `-sign` works with `private.pem` because the private key creates the signature.