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smime(1ssl)
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.
-sign Signs 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 Verifies 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.
-text 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.
-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.
-nosigs Does 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
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
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
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