NOTES

The MIME message must be sent without any blank lines between the headers and the output. Some mail programs will automatically add a blank line. Piping the mail directly to sendmail is one way to achieve the correct format.

The supplied message to be signed or encrypted must include the necessary MIME headers or many S/MIME clients won't display it properly (if at all). You can use the -text option to automatically add plain text headers.

A "signed and encrypted" message is one where a signed message is then encrypted. This can be produced by encrypting an already signed message: see the examples section.

This version of the program only allows one signer per message but it will verify multiple signers on received messages. Some S/MIME clients choke if a message contains multiple signers. It is possible to sign messages "in parallel" by signing an already signed message.

The options -encrypt and -decrypt reflect common usage in S/MIME clients. Strictly speaking these process PKCS#7 enveloped data: PKCS#7 encrypted data is used for other purposes.

The -resign option uses an existing message digest when adding a new signer. This means that attributes must be present in at least one existing signer using the same message digest or this operation will fail.

The -stream and -indef options enable streaming I/O support. As a result the encoding is BER using indefinite length constructed encoding and no longer DER. Streaming is supported for the -encrypt operation and the -sign operation if the content is not detached.

Streaming is always used for the -sign operation with detached data but since the content is no longer part of the PKCS#7 structure the encoding remains DER.

EXIT CODES

0

The operation was completely successfully.

1

An error occurred parsing the command options.

2

One of the input files could not be read.

3

An error occurred creating the PKCS#7 file or when reading the MIME message.

4

An error occurred decrypting or verifying the message.

5

The message was verified correctly but an error occurred writing out the signers certificates.

EXAMPLES

Create a cleartext signed message:

 openssl smime -sign -in message.txt -text -out mail.msg \
        -signer mycert.pem

Create an opaque signed message:

 openssl smime -sign -in message.txt -text -out mail.msg -nodetach \
        -signer mycert.pem

Create a signed message, include some additional certificates and read the private key from another file:

 openssl smime -sign -in in.txt -text -out mail.msg \
        -signer mycert.pem -inkey mykey.pem -certfile mycerts.pem

Create a signed message with two signers:

 openssl smime -sign -in message.txt -text -out mail.msg \
        -signer mycert.pem -signer othercert.pem

Send a signed message under Unix directly to sendmail, including headers:

 openssl smime -sign -in in.txt -text -signer mycert.pem \
        -from steve@openssl.org -to someone@somewhere \
        -subject "Signed message" | sendmail someone@somewhere

Verify a message and extract the signer's certificate if successful:

 openssl smime -verify -in mail.msg -signer user.pem -out signedtext.txt

Send encrypted mail using triple DES:

 openssl smime -encrypt -in in.txt -from steve@openssl.org \
        -to someone@somewhere -subject "Encrypted message" \
        -des3 user.pem -out mail.msg

Sign and encrypt mail:

 openssl smime -sign -in ml.txt -signer my.pem -text \
        | openssl smime -encrypt -out mail.msg \
        -from steve@openssl.org -to someone@somewhere \
        -subject "Signed and Encrypted message" -des3 user.pem

Note: the encryption command does not include the -text option because the message being encrypted already has MIME headers.

Decrypt mail:

 openssl smime -decrypt -in mail.msg -recip mycert.pem -inkey key.pem

The output from Netscape form signing is a PKCS#7 structure with the detached signature format. You can use this program to verify the signature by line wrapping the base64 encoded structure and surrounding it with:

 -----BEGIN PKCS7-----
 -----END PKCS7-----

and using the command:

 openssl smime -verify -inform PEM -in signature.pem -content content.txt

Alternatively you can base64 decode the signature and use:

 openssl smime -verify -inform DER -in signature.der -content content.txt

Create an encrypted message using 128 bit Camellia:

 openssl smime -encrypt -in plain.txt -camellia128 -out mail.msg cert.pem

Add a signer to an existing message:

 openssl smime -resign -in mail.msg -signer newsign.pem -out mail2.msg

BUGS

The MIME parser isn't very clever: it seems to handle most messages that I've thrown at it but it may choke on others.

The code currently will only write out the signer's certificate to a file: if the signer has a separate encryption certificate this must be manually extracted. There should be some heuristic that determines the correct encryption certificate.

Ideally a database should be maintained of a certificates for each email address.

The code doesn't currently take note of the permitted symmetric encryption algorithms as supplied in the SMIMECapabilities signed attribute. This means the user has to manually include the correct encryption algorithm. It should store the list of permitted ciphers in a database and only use those.

No revocation checking is done on the signer's certificate.

The current code can only handle S/MIME v2 messages, the more complex S/MIME v3 structures may cause parsing errors.

SEE ALSO

The -no_alt_chains option was added in OpenSSL 1.1.0.

COPYRIGHT

Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.