smime - S/MIME utility
The B<smime> command handles S/MIME mail. It can encrypt, decrypt, sign and
verify S/MIME messages.
=head1 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 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 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 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.
=item B<-in filename>
the input message to be encrypted or signed or the MIME message to
be decrypted or verified.
=item B<-inform SMIME|PEM|DER>
this specifies the input format for the PKCS#7 structure. The default
is B<SMIME> which reads an S/MIME format message. B<PEM> and B<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
B<-encrypt> or B<-sign>) this option has no effect.
=item B<-out filename>
the message text that has been decrypted or verified or the output MIME
format message that has been signed or verified.
=item B<-outform SMIME|PEM|DER>
this specifies the output format for the PKCS#7 structure. The default
is B<SMIME> which write an S/MIME format message. B<PEM> and B<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
B<-verify> or B<-decrypt>) this option has no effect.
=item B<-stream -indef -noindef>
the B<-stream> and B<-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 B<SMIME> it is currently off by default for all
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.
=item B<-content filename>
This specifies a file containing the detached content, this is only
useful with the B<-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.
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.
=item B<-CAfile file>
a file containing trusted CA certificates, only used with B<-verify>.
=item B<-CApath dir>
a directory containing trusted CA certificates, only used with
B<-verify>. This directory must be a standard certificate directory: that
is a hash of each subject name (using B<x509 -hash>) should be linked
to each certificate.
=item B<-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).
the encryption algorithm to use. For example DES (56 bits) - B<-des>,
triple DES (168 bits) - B<-des3>,
EVP_get_cipherbyname() function) can also be used preceded by a dash, for
example B<-aes_128_cbc>. See L<B<enc>|enc(1)> for list of ciphers
supported by your version of OpenSSL.
If not specified triple DES is used. Only used with B<-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 B<-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 B<-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 included.
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.
=item B<-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.
=item B<-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.
=item B<-recip file>
the recipients certificate when decrypting a message. This certificate
must match one of the recipients of the message or an error occurs.
=item B<-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 B<-recip> or B<-signer> file. When signing this option can be used
multiple times to specify successive keys.
=item B<-passin arg>
the private key password source. For more information about the format of B<arg>
see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
=item B<-rand file(s)>
a file or files containing random data used to seed the random number
generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
Multiple files can be specified separated by a OS-dependent character.
The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
one or more certificates of message recipients: used when encrypting
=item B<-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.
=item B<-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
L<B<verify>|verify(1)> manual page for details.
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 B<-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 B<-encrypt> and B<-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 B<-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 B<-stream> and B<-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 B<-encrypt> operation and the
B<-sign> operation if the content is not detached.
Streaming is always used for the B<-sign> operation with detached data but
since the content is no longer part of the PKCS#7 structure the encoding
=head1 EXIT CODES
the operation was completely successfully.
an error occurred parsing the command options.
one of the input files could not be read.
an error occurred creating the PKCS#7 file or when reading the MIME
an error occurred decrypting or verifying the message.
the message was verified correctly but an error occurred writing out
the signers certificates.
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 firstname.lastname@example.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 email@example.com \
-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 firstname.lastname@example.org -to someone@somewhere \
-subject "Signed and Encrypted message" -des3 user.pem
Note: the encryption command does not include the B<-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
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
Ideally a database should be maintained of a certificates for each email
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 B<-signer> options and the B<-resign> command were first
added in OpenSSL 1.0.0
The -no_alt_chains options was first added to OpenSSL 1.0.2b.