SMIME(1) OpenSSL SMIME(1)
NAME
smime - S/MIME utility
SYNOPSIS
openssl smime [-encrypt] [-decrypt] [-sign] [-resign] [-verify]
[-pk7out] [-[cipher]] [-in file] [-CAfile file] [-CApath dir]
[-trusted_first] [-no_alt_chains] [-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] [-indef] [-noindef] [-stream] [-rand file(s)]
[-md digest] [cert.pem]...
DESCRIPTION
The smime command handles S/MIME mail. It can encrypt, decrypt, sign
and verify S/MIME messages.
COMMAND OPTIONS
There are six 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.
Note that no revocation check is done for the recipient cert, so if
that key has been compromised, others may be able to decrypt the
text.
-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.
-resign
resign a message: take an existing message and one or more new
signers.
-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.
-stream -indef -noindef
the -stream and -indef options are equivalent and enable streaming
I/O for encoding operations. This permits single pass processing of
data without the need to hold the entire contents in memory,
potentially supporting very large files. Streaming is automatically
set for S/MIME signing with detached data if the output format is
SMIME it is currently off by default for all other operations.
-noindef
disable streaming I/O where it would produce and indefinite length
constructed encoding. This option currently has no effect. In
future streaming will be enabled by default on all relevant
operations and this option will disable it.
-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.
-trusted_first
Use certificates in CA file or CA directory over certificates
provided in the message when building the trust chain to verify a
certificate. This is mainly useful in environments with Bridge CA
or Cross-Certified CAs.
-md digest
digest algorithm to use when signing or resigning. If not present
then the default digest algorithm for the signing key will be used
(usually SHA1).
-[cipher]
the encryption algorithm to use. For example DES (56 bits) - -des,
triple DES (168 bits) - -des3, EVP_get_cipherbyname() function) can
also be used preceded by a dash, for example -aes_128_cbc. See enc
for list of ciphers supported by your version of OpenSSL.
If not specified triple DES 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
a signing certificate when signing or resigning a message, this
option can be used multiple times if more than one signer is
required. 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. When signing this option can be
used multiple times to specify successive keys.
-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.
-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all,
-policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig
-no_alt_chains
Set various options of certificate chain verification. See verify
manual page for details.
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.
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 experimental 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 AT 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 AT 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 AT 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.
HISTORY
The use of multiple -signer options and the -resign command were first
added in OpenSSL 1.0.0
The -no_alt_chains options was first added to OpenSSL 1.0.2b.
1.0.2k 2023-11-13 SMIME(1)
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