The smime command handles S/MIME mail. It can encrypt, decrypt, sign and
verify S/MIME messages.
COMMAND OPTIONS
There are five operation options that set the type of operation to be performed.
The meaning of the other options varies according to the operation type.
-encrypt
encrypt 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
decrypt 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.
-sign
sign 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.
-verify
verify 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.
-in filename
the input message to be encrypted or signed or the MIME message to
be decrypted or verified.
-inform SMIME|PEM|DER
this specifies the input format for the PKCS#7 structure. The default
is SMIME which reads an S/MIME format message. PEM and DER
format change this to expect PEM and DER format PKCS#7 structures
instead. This currently only affects the input format of the PKCS#7
structure, if no PKCS#7 structure is being input (for example with
-encrypt or -sign) this option has no effect.
-out filename
the message text that has been decrypted or verified or the output MIME
format message that has been signed or verified.
-outform SMIME|PEM|DER
this specifies the output format for the PKCS#7 structure. The default
is SMIME which write an S/MIME format message. PEM and DER
format change this to write PEM and DER format PKCS#7 structures
instead. This currently only affects the output format of the PKCS#7
structure, if no PKCS#7 structure is being output (for example with
-verify or -decrypt) this option has no effect.
-content filename
This specifies a file containing the detached content, this is only
useful with the -verify command. 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.
-text
this option adds 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.
-CAfile file
a file containing trusted CA certificates, only used with -verify.
-CApath dir
a directory containing trusted CA certificates, only used with
-verify. This directory must be a standard certificate directory: that
is a hash of each subject name (using x509 -hash) should be linked
to each certificate.
the encryption algorithm to use. DES (56 bits), triple DES (168 bits),
40, 64 or 128 bit RC2 or 128, 192 or 256 bit AES respectively. If not
specified 40 bit RC2 is used. Only used with -encrypt.
-nointern
when verifying a message normally 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
do not verify the signers certificate of a signed message.
-nochain
do not do chain verification of signers certificates: that is don't
use the certificates in the signed message as untrusted CAs.
-nosigs
don't try to verify the signatures on the message.
-nocerts
when signing a message the signer's certificate is normally included
with this option it is excluded. This will reduce the size of the
signed message but the verifier must have a copy of the signers certificate
available locally (passed using the -certfile option for example).
-noattr
normally when a message is signed a set of attributes are included which
include the signing time and supported symmetric algorithms. With this
option they are not included.
-binary
normally 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. When this option is present no translation occurs. This
is useful when handling binary data which may not be in MIME format.
-nodetach
when signing a message use opaque signing: 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.
-certfile file
allows additional certificates to be specified. When signing these will
be included with the message. When verifying these will be searched for
the signers certificates. The certificates should be in PEM format.
-signer file
the signers certificate when signing a message. If a message is
being verified then the signers certificates will be written to this
file if the verification was successful.
-recip file
the recipients certificate when decrypting a message. This certificate
must match one of the recipients of the message or an error occurs.
-inkey file
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 -signer file.
-passin arg
the private key password source. For more information about the format of arg
see the PASSPHRASEARGUMENTS section in openssl(1).
-rand file(s)
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 specified separated by a OS-dependent character.
The separator is ; for MS-Windows, , for OpenVMS, and : 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 the signers certificate's email
address matches that specified in the From: address.
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 wont 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.
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.
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:
alternatively you can base64 decode the signature and use
openssl smime -verify -inform DER -in signature.der -content content.txt
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.
