smime(1)
SMIME(1) 0.9.6h (2002-11-09) SMIME(1)
NAME
smime - S/MIME utility
SYNOPSIS
openssl smime [-encrypt] [-decrypt] [-sign] [-verify]
[-pk7out] [-des] [-des3] [-rc2-40] [-rc2-64] [-rc2-128] [-in
file] [-certfile file] [-signer file] [-recip file]
[-inform SMIME|PEM|DER] [-passin arg] [-inkey file] [-out
file] [-outform SMIME|PEM|DER] [-content file] [-to addr]
[-from ad] [-subject s] [-text] [-rand file(s)]
[cert.pem]...
DESCRIPTION
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
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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.
-des -des3 -rc2-40 -rc2-64 -rc2-128
the encryption algorithm to use. DES (56 bits), triple
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DES (168 bits) or 40, 64 or 128 bit RC2 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.
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SMIME(1) 0.9.6h (2002-11-09) SMIME(1)
-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 PASS PHRASE ARGUMENTS
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.
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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
o 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 and 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
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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
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.
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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.
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