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SMIME(1) OpenSSL SMIME(1)
NAME
smime - S/MIME utility
SYNOPSIS
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]
[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.
-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.
-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 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.
-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
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 steveATopenssl.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 steveATopenssl.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 steveATopenssl.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
1.0.0e 2010-10-04 SMIME(1)
