NAME¶
cms - CMS utility
SYNOPSIS¶
openssl cms [
-encrypt] [
-decrypt] [
-sign]
[
-verify] [
-cmsout] [
-resign] [
-data_create] [
-data_out] [
-digest_create] [
-digest_verify] [
-compress] [
-uncompress] [
-EncryptedData_encrypt] [
-sign_receipt] [
-verify_receipt receipt] [
-in filename]
[
-inform SMIME|PEM|DER] [
-rctform SMIME|PEM|DER] [
-out
filename] [
-outform SMIME|PEM|DER] [
-stream -indef
-noindef] [
-noindef] [
-content filename] [
-text] [
-noout] [
-print] [
-CAfile file] [
-CApath dir] [
-no_alt_chains] [
-md digest] [
-[cipher]] [
-nointern] [
-no_signer_cert_verify] [
-nocerts] [
-noattr] [
-nosmimecap] [
-binary] [
-nodetach] [
-certfile file] [
-certsout file] [
-signer file] [
-recip file] [
-keyid] [
-receipt_request_all
-receipt_request_first] [
-receipt_request_from emailaddress] [
-receipt_request_to emailaddress] [
-receipt_request_print] [
-secretkey key] [
-secretkeyid id] [
-econtent_type type]
[
-inkey file] [
-keyopt name:parameter] [
-passin arg] [
-rand file(s)] [
cert.pem...] [
-to addr] [
-from
addr] [
-subject subj] [cert.pem]...
DESCRIPTION¶
The
cms command handles S/MIME v3.1 mail. It can encrypt, decrypt, sign
and verify, compress and uncompress S/MIME messages.
COMMAND OPTIONS¶
There are fourteen 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. The actual CMS type is <B>EnvelopedData<B>.
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.
- -debug_decrypt
- this option sets the CMS_DEBUG_DECRYPT flag. This option should be
used with caution: see the notes section below.
- -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.
- -cmsout
- takes an input message and writes out a PEM encoded CMS structure.
- -resign
- resign a message: take an existing message and one or more new
signers.
- -data_create
- Create a CMS Data type.
- -data_out
- Data type and output the content.
- -digest_create
- Create a CMS DigestedData type.
- -digest_verify
- Verify a CMS DigestedData type and output the content.
- -compress
- Create a CMS CompressedData type. OpenSSL must be compiled with
zlib support for this option to work, otherwise it will output an
error.
- -uncompress
- Uncompress a CMS CompressedData type and output the content.
OpenSSL must be compiled with zlib support for this option to work,
otherwise it will output an error.
- -EncryptedData_encrypt
- Encrypt content using supplied symmetric key and algorithm using a CMS
EncrytedData type and output the content.
- -sign_receipt
- Generate and output a signed receipt for the supplied message. The input
message must contain a signed receipt request. Functionality is
otherwise similar to the -sign operation.
- -verify_receipt receipt
- Verify a signed receipt in filename receipt. The input message
must contain the original receipt request. Functionality is
otherwise similar to the -verify operation.
- -in filename
- the input message to be encrypted or signed or the message to be decrypted
or verified.
- -inform SMIME|PEM|DER
- this specifies the input format for the CMS structure. The default is
SMIME which reads an S/MIME format message. PEM and
DER format change this to expect PEM and DER format CMS structures
instead. This currently only affects the input format of the CMS
structure, if no CMS structure is being input (for example with
-encrypt or -sign) this option has no effect.
- -rctform SMIME|PEM|DER
- specify the format for a signed receipt for use with the
-receipt_verify operation.
- -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 CMS structure. The default is
SMIME which writes an S/MIME format message. PEM and
DER format change this to write PEM and DER format CMS structures
instead. This currently only affects the output format of the CMS
structure, if no CMS 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 CMS 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.
- -noout
- for the -cmsout operation do not output the parsed CMS structure.
This is useful when combined with the -print option or if the
syntax of the CMS structure is being checked.
- -print
- for the -cmsout operation print out all fields of the CMS
structure. This is mainly useful for testing purposes.
- -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 triple DES (168 bits) -
-des3 or 256 bit AES - -aes256. Any standard algorithm name
(as used by the EVP_get_cipherbyname() function) can also be used
preceded by a dash, for example -aes_128_cbc. See enc for a
list of ciphers supported by your version of OpenSSL.
If not specified triple DES is used. Only used with -encrypt and
-EncryptedData_create commands.
- -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.
- -no_signer_cert_verify
- do not verify the signers certificate of a signed 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.
- -nosmimecap
- exclude the list of supported algorithms from signed attributes, other
options such as signing time and content type are still 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.
- -certsout file
- any certificates contained in the message are written to file.
- -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
- when decrypting a message this specifies the recipients certificate. The
certificate must match one of the recipients of the message or an error
occurs.
When encrypting a message this option may be used multiple times to specify
each recipient. This form must be used if customised parameters are
required (for example to specify RSA-OAEP).
- -keyid
- use subject key identifier to identify certificates instead of issuer name
and serial number. The supplied certificate must include a subject
key identifier extension. Supported by -sign and -encrypt
options.
- -receipt_request_all -receipt_request_first
- for -sign option include a signed receipt request. Indicate
requests should be provided by all receipient or first tier recipients
(those mailed directly and not from a mailing list). Ignored it
-receipt_request_from is included.
- -receipt_request_from emailaddress
- for -sign option include a signed receipt request. Add an explicit
email address where receipts should be supplied.
- -receipt_request_to emailaddress
- Add an explicit email address where signed receipts should be sent to.
This option must but supplied if a signed receipt it
requested.
- -receipt_request_print
- For the -verify operation print out the contents of any signed
receipt requests.
- -secretkey key
- specify symmetric key to use. The key must be supplied in hex format and
be consistent with the algorithm used. Supported by the
-EncryptedData_encrypt -EncrryptedData_decrypt,
-encrypt and -decrypt options. When used with
-encrypt or -decrypt the supplied key is used to wrap or
unwrap the content encryption key using an AES key in the
KEKRecipientInfo type.
- -secretkeyid id
- the key identifier for the supplied symmetric key for
KEKRecipientInfo type. This option must be present if the
-secretkey option is used with -encrypt. With
-decrypt operations the id is used to locate the relevant
key if it is not supplied then an attempt is used to decrypt any
KEKRecipientInfo structures.
- -econtent_type type
- set the encapsulated content type to type if not supplied the
Data type is used. The type argument can be any valid OID
name in either text or numerical format.
- -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.
- -keyopt name:opt
- for signing and encryption this option can be used multiple times to set
customised parameters for the preceding key or certificate. It can
currently be used to set RSA-PSS for signing, RSA-OAEP for encryption or
to modify default parameters for ECDH.
- -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 certificate chain valiadition option. See the 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 CMS enveloped data: CMS 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 CMS structure the encoding remains
DER.
If the
-decrypt option is used without a recipient certificate then an
attempt is made to locate the recipient by trying each potential recipient in
turn using the supplied private key. To thwart the MMA attack
(Bleichenbacher's attack on PKCS #1 v1.5 RSA padding) all recipients are tried
whether they succeed or not and if no recipients match the message is
"decrypted" using a random key which will typically output garbage.
The
-debug_decrypt option can be used to disable the MMA attack
protection and return an error if no recipient can be found: this option
should be used with caution. For a fuller description see
CMS_decrypt(3)).
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 CMS 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.
The
smime utility can only process the older
PKCS#7 format. The
cms utility supports Cryptographic Message Syntax format. Use of some
features will result in messages which cannot be processed by applications
which only support the older format. These are detailed below.
The use of the
-keyid option with
-sign or
-encrypt.
The
-outform PEM option uses different headers.
The
-compress option.
The
-secretkey option when used with
-encrypt.
The use of PSS with
-sign.
The use of OAEP or non-RSA keys with
-encrypt.
Additionally the
-EncryptedData_create and
-data_create type
cannot be processed by the older
smime command.
EXAMPLES¶
Create a cleartext signed message:
openssl cms -sign -in message.txt -text -out mail.msg \
-signer mycert.pem
Create an opaque signed message
openssl cms -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 cms -sign -in in.txt -text -out mail.msg \
-signer mycert.pem -inkey mykey.pem -certfile mycerts.pem
Create a signed message with two signers, use key identifier:
openssl cms -sign -in message.txt -text -out mail.msg \
-signer mycert.pem -signer othercert.pem -keyid
Send a signed message under Unix directly to sendmail, including headers:
openssl cms -sign -in in.txt -text -signer mycert.pem \
-from steve@openssl.org -to someone@somewhere \
-subject "Signed message" | sendmail someone@somewhere
Verify a message and extract the signer's certificate if successful:
openssl cms -verify -in mail.msg -signer user.pem -out signedtext.txt
Send encrypted mail using triple DES:
openssl cms -encrypt -in in.txt -from steve@openssl.org \
-to someone@somewhere -subject "Encrypted message" \
-des3 user.pem -out mail.msg
Sign and encrypt mail:
openssl cms -sign -in ml.txt -signer my.pem -text \
| openssl cms -encrypt -out mail.msg \
-from steve@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 cms -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 cms -verify -inform PEM -in signature.pem -content content.txt
alternatively you can base64 decode the signature and use
openssl cms -verify -inform DER -in signature.der -content content.txt
Create an encrypted message using 128 bit Camellia:
openssl cms -encrypt -in plain.txt -camellia128 -out mail.msg cert.pem
Add a signer to an existing message:
openssl cms -resign -in mail.msg -signer newsign.pem -out mail2.msg
Sign mail using RSA-PSS:
openssl cms -sign -in message.txt -text -out mail.msg \
-signer mycert.pem -keyopt rsa_padding_mode:pss
Create encrypted mail using RSA-OAEP:
openssl cms -encrypt -in plain.txt -out mail.msg \
-recip cert.pem -keyopt rsa_padding_mode:oaep
Use SHA256 KDF with an ECDH certificate:
openssl cms -encrypt -in plain.txt -out mail.msg \
-recip ecdhcert.pem -keyopt ecdh_kdf_md:sha256
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.
HISTORY¶
The use of multiple
-signer options and the
-resign command were
first added in OpenSSL 1.0.0
The
keyopt option was first added in OpenSSL 1.1.0
The use of
-recip to specify the recipient when encrypting mail was first
added to OpenSSL 1.1.0
Support for RSA-OAEP and RSA-PSS was first added to OpenSSL 1.1.0.
The use of non-RSA keys with
-encrypt and
-decrypt was first added
to OpenSSL 1.1.0.
The -no_alt_chains options was first added to OpenSSL 1.0.2b.