smime - S/MIME utility
[-encrypt] [-decrypt] [-sign] [-resign] [-verify] [-pk7out] [-des] [-des3] [-rc2-40] [-rc2-64] [-rc2-128] [-aes128] [-aes192] [-aes256] [-camellia128] [-camellia192] [-camellia256] [-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] [-rand file(s)] [-md digest] [cert.pem]...
The smime command handles S/MIME mail. It can encrypt, decrypt, sign and verify
There are five operation options that set the type of operation to be
performed. The meaning of the other options varies according to the
encrypt mail for the given recipient certificates. Input file is the
message to be encrypted. The output file is the encrypted mail in MIME
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
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.
- -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.
- -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.
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).
- -des -des3 -rc2-40 -rc2-64 -rc2-128 -aes128 -aes192 -aes256 -camellia128 -camellia192 -camellia256
the encryption algorithm to use. DES (56 bits), triple DES (168 bits), 40,
64 or 128 bit RC2, 128, 192 or 256 bit AES, or 128, 192 or 256 bit Camellia
respectively. Any other cipher name (as recognized by the
EVP_get_cipherbyname() function) can also be used preceded by
a dash, for example -aes_128_cbc.
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
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 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.
- -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
- -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.
one or more certificates of message recipients: used when encrypting a
- -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.
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
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 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
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
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
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 0.9.9