NAME

smime − S/MIME utility

SYNOPSIS

openssl smime [−encrypt] [−decrypt] [−sign] [−verify] [−pk7out] [−des] [−des3] [−rc2-40] [−rc2-64] [−rc2-128] [−certfile filename] [−signer filename] [−recip filename] [−infile] [−informSMIME | PEM | DER] [−passin arg] [−inkey filename] [−outfile] [−outform SMIME | PEM | DER] [−content filename] [−to addr] [−fromad] [−subject s] [−text] [−rand filename] [cert.pem ...]

OPTIONS

There are five options that set the type of operation to be performed.  The meaning of the other options varies according to the operation type. 

−encrypt
Encrypts mail for the given recipient certificates. Input file is the message to be encrypted. The output file is the encrypted mail in MIME format.

−decrypt
Decrypts mail using the supplied certificate and private key. Expects an encrypted mail message in MIME format for the input file. The decrypted mail is written to the output file.

−signSigns mail using the supplied certificate and private key. Input file is the message to be signed. The signed message in MIME format is written to the output file. 

−verifyVerifies signed mail.  Expects a signed mail message on input, and outputs the signed data. Both clear text and opaque signing is supported. 

−pk7out
Takes an input message and writes out a PEM encoded PKCS#7 structure. 

−infilename
The input message to be encrypted or signed, or the MIME message to be decrypted or verified.

−informSMIME|PEM|DER
Specifies the input format for the PKCS#7 structure. The default is SMIME which reads an S/MIME format message. The PEM and the DER format change this to expect PEM and DER format PKCS#7 structures instead. This only affects the input format of the PKCS#7 structure. If no PKCS#7 structure is  input, such as −encrypt or −sign, this option has no effect. 

−outfilename
The message text that has been decrypted or verified or the output MIME format message that has been signed or verified.

−outformSMIME|PEM|DER
Specifies the output format for the PKCS#7 structure. The default is SMIME which writes an S/MIME format message. The PEM and DER format change this to write PEM and DER format PKCS#7 structures instead. This only affects the output format of the PKCS#7 structure. If no PKCS#7 structure is  output, such as −verify or −decrypt, this option has no effect. 

−contentfilename
Specifies a file containing the detached content. This is only useful with the −verify option. This is only usable if the PKCS#7 structure is using the detached signature form where the content is not included.  This option will override any content if the input format is S/MIME and it uses the multipart/signed MIME content type. 

−textAdds plain text (text/plain) MIME headers to the supplied message if encrypting or signing. If decrypting or verifying it strips off text headers. If the decrypted or verified message is not of MIME  type text/plain then an error occurs. 

−CAfilefile
A file containing trusted CA certificates. It is only used with the −verify option. 

−CApathdir
A directory containing trusted CA certificates. It is only used with the −verify option. This directory must be a standard certificate directory, meaning a hash of each subject name (using x509 -hash) should be linked to each certificate. 

−des−des3−rc2-40−rc2-64−rc2-128
The encryption algorithm to use. DES (56 bits), triple DES (168 bits) or 40, 64 or 128 bit RC2, respectively. If not specified, 40−bit RC2 is used. These are used only with the −encrypt option. 

−nointern
When verifying a message, certificates (if any) included in the message are searched for the signing certificate. With this option only the certificates specified in the −certfile option are used. The supplied certificates can still be used as untrusted CAs however. 

−noverify
Does not verify the signers certificate of a signed message.

−nochain
Does not perform chain verification of signers certificates. That is, it does not  use the certificates in the signed message as untrusted CAs.

−nosigsDoes not try to verify the signatures on the message. 

−nocerts
When signing a message, the signer’s certificate is usually included. With this option the signer’s certificate is excluded. This will reduce the size of the signed message, but the verifier must have a copy of the signer’s certificate available locally (passed using the −certfile option, for example). 

−noattr
When a message is signed, a set of attributes is included, such as the signing time and supported symmetric algorithms. With this option they are not included.

−binary
Usually the input message is converted to canonical format, which is effectively using CR and LF as end-of-line, as required by the S/MIME specification. With this option  no translation occurs. This is useful when handling binary data which may not be in MIME format.

−nodetach
Uses opaque signing when signing a message. This form is more resistant to translation by mail relays, but it cannot be read by mail agents that do not support S/MIME. Without this option cleartext signing with the MIME type multipart/signed is used.

−certfilefilename
Allows additional certificates to be specified. When signing these will be included with the message. When verifying, these will be searched for the signer’s certificates. The certificates should be in PEM format. 

−signerfilename
The signer’s certificate when signing a message. If a message is being verified then the signer’s certificates will be written to this file if the verification was successful.

−recipfilename
The recipient’s certificate when decrypting a message. This certificate must match one of the recipient’s of the message or an error occurs.

−inkeyfilename
The private key to use when signing or decrypting. This must match the corresponding certificate. If this option is not specified then the private key must be included in the certificate file specified with the −recip or the −signer option. 

−passinarg
The private key password source. For more information about the format of arg, see the Pass Phrase Arguments section in openssl(1ssl). 

−randfilename
A file or files containing random data used to seed the random number generator, or an EGD socket. (See RAND_egd(3).) Multiple files can be separated by an OS-dependent character. The separator is a semicolon (;) for MS-Windows, a comma (,) for OpenVMS, and a colon (:) for all others. 

cert.pem...
One or more certificates of message recipients, used when encrypting a message.

−to, −from, −subject
The relevant mail headers. These are included outside the signed portion of a message so they may be included manually. If signing, then many S/MIME mail clients check that the signer’s certificate email address matches that specified in the From: address. 

DESCRIPTION

The smime command handles S/MIME mail. It can encrypt, decrypt, sign and verify S/MIME messages. 

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 will not 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. 

This version of the program only allows one signer per message, but it will verify multiple signers on received messages. Some S/MIME clients fail 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. These process PKCS#7 enveloped data. The PKCS#7 encrypted data is used for other purposes. 

RESTRICTIONS

The MIME parser is not very clever. It seems to handle most messages, but it may fail on others. 

The code 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 certificate database should be maintained for each email address. 

The code does not 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 code can only handle S/MIME v2 messages. The more complex S/MIME v3 structures may cause parsing errors. 

EXIT STATUS

0The operation was completely successfully. 

1An error occurred parsing the command options. 

2One of the input files could not be read. 

3An error occurred creating the PKCS#7 file or when reading the MIME message. 

4An error occurred decrypting or verifying the message. 

5The 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

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

Notice that 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 the following lines:

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

You should then use the following command:

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

Alternatively, you can base64 decode the signature and use the following command:

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