SMIME(1) OpenSSL SMIME(1)
smime - S/MIME utility
openssl smime [-encrypt] [-decrypt] [-sign] [-resign] [-verify] [-pk7out] [-[cipher]] [-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] [-indef] [-noindef] [-stream] [-rand file(s)] [-md digest]
The smime command handles S/MIME mail. It can encrypt, decrypt, sign and verify S/MIME
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 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 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
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 signed mail. Expects a signed mail message on input and outputs the signed
data. Both clear text and opaque signing is supported.
takes an input message and writes out a PEM encoded PKCS#7 structure.
resign a message: take an existing message and one or more new signers.
the input message to be encrypted or signed or the MIME message to be decrypted or
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.
the message text that has been decrypted or verified or the output MIME format message
that has been signed or verified.
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.
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.
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
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.
a file containing trusted CA certificates, only used with -verify.
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.
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).
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
If not specified 40 bit RC2 is used. Only used with -encrypt.
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.
do not verify the signers certificate of a signed message.
do not do chain verification of signers certificates: that is don't use the
certificates in the signed message as untrusted CAs.
don't try to verify the signatures on the message.
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).
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
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.
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.
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.
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
the recipients certificate when decrypting a message. This certificate must match one
of the recipients of the message or an error occurs.
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.
the private key password source. For more information about the format of arg see the
PASS PHRASE ARGUMENTS section in openssl(1).
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
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
Set various options of certificate chain verification. See verify manual page for
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
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
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
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.
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
Create a cleartext signed message:
openssl smime -sign -in message.txt -text -out mail.msg \
Create an opaque signed message
openssl smime -sign -in message.txt -text -out mail.msg -nodetach \
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 email@example.com -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 firstname.lastname@example.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 email@example.com -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.
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:
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
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.
The use of multiple -signer options and the -resign command were first added in OpenSSL
1.0.0 2009-09-30 SMIME(1)