pyhanko.sign.signers.pdf_cms module¶

This module defines utility classes to format CMS objects for use in PDF signatures.

class pyhanko.sign.signers.pdf_cms.Signer(prefer_pss=False)¶

Bases: object

Abstract signer object that is agnostic as to where the cryptographic operations actually happen.

As of now, pyHanko provides two implementations:

SimpleSigner implements the easy case where all the key material can be loaded into memory.
PKCS11Signer implements a signer that is capable of interfacing with a PKCS11 device (see also BEIDSigner).

Parameters: prefer_pss – When signing using an RSA key, prefer PSS padding to legacy PKCS#1 v1.5 padding. Default is False. This option has no effect on non-RSA signatures.

signing_cert: asn1crypto.x509.Certificate¶: The certificate that will be used to create the signature.

cert_registry: pyhanko.sign.general.CertificateStore¶: Collection of certificates associated with this signer. Note that this is simply a bookkeeping tool; in particular it doesn’t care about trust.

signature_mechanism: asn1crypto.algos.SignedDigestAlgorithm = None¶: The (cryptographic) signature mechanism to use.

get_signature_mechanism(digest_algorithm)¶

Get the signature mechanism for this signer to use. If signature_mechanism is set, it will be used. Otherwise, this method will attempt to put together a default based on mechanism used in the signer’s certificate.

Parameters: digest_algorithm – Digest algorithm to use as part of the signature mechanism. Only used if a signature mechanism object has to be put together on-the-fly, and the digest algorithm could not be inferred from the signer’s certificate.
Returns: A SignedDigestAlgorithm object.

sign_raw(data: bytes, digest_algorithm: str, dry_run=False) → bytes¶

Compute the raw cryptographic signature of the data provided, hashed using the digest algorithm provided.

Parameters

data – Data to sign.
digest_algorithm –
Digest algorithm to use.

Warning

If signature_mechanism also specifies a digest, they should match.
dry_run – Do not actually create a signature, but merely output placeholder bytes that would suffice to contain an actual signature.

Returns

Signature bytes.

property subject_name¶

Returns: The subject’s common name as a string, extracted from signing_cert.

static format_revinfo(ocsp_responses: Optional[list] = None, crls: Optional[list] = None)¶

Format Adobe-style revocation information for inclusion into a CMS object.

Parameters

ocsp_responses – A list of OCSP responses to include.
crls – A list of CRLs to include.

Returns

A CMS attribute containing the relevant data.

signed_attrs(data_digest: bytes, digest_algorithm: str, timestamp: Optional[datetime.datetime] = None, content_type='data', revocation_info=None, use_pades=False, cades_meta: Optional[pyhanko.sign.ades.api.CAdESSignedAttrSpec] = None, timestamper=None, dry_run=False)¶

Changed in version 0.4.0: Added positional digest_algorithm parameter _(breaking change)_.

Changed in version 0.5.0: Added dry_run, timestamper and cades_meta parameters.

Format the signed attributes for a CMS signature.

Parameters

data_digest – Raw digest of the data to be signed.
digest_algorithm –

New in version 0.4.0.

Name of the digest algorithm used to compute the digest.
timestamp – Current timestamp (ignored when use_pades is True).
revocation_info – Revocation information to embed; this should be the output of a call to Signer.format_revinfo() or None (ignored when use_pades is True).
use_pades – Respect PAdES requirements.
dry_run –

New in version 0.5.0.

Flag indicating “dry run” mode. If True, only the approximate size of the output matters, so cryptographic operations can be replaced by placeholders.
timestamper –

New in version 0.5.0.

Timestamper to use when creating timestamp tokens.
cades_meta –

New in version 0.5.0.

Specification for CAdES-specific attributes.
content_type –
CMS content type of the encapsulated data. Default is data.

Danger

This parameter is internal API, and non-default values must not be used to produce PDF signatures.

Returns

An asn1crypto.cms.CMSAttributes object.

unsigned_attrs(digest_algorithm, signature: bytes, timestamper=None, dry_run=False) → Optional[asn1crypto.cms.CMSAttributes]¶

Compute the unsigned attributes to embed into the CMS object. This function is called after signing the hash of the signed attributes (see signed_attrs()).

By default, this method only handles timestamp requests, but other functionality may be added by subclasses

If this method returns None, no unsigned attributes will be embedded.

Parameters

digest_algorithm – Digest algorithm used to hash the signed attributes.
signature – Signature of the signed attribute hash.
timestamper – Timestamp supplier to use.
dry_run – Flag indicating “dry run” mode. If True, only the approximate size of the output matters, so cryptographic operations can be replaced by placeholders.

Returns

The unsigned attributes to add, or None.

signer_info(digest_algorithm: str, signed_attrs, signature)¶

Format the SignerInfo entry for a CMS signature.

Parameters

digest_algorithm – Digest algorithm to use.
signed_attrs – Signed attributes (see signed_attrs()).
signature – The raw signature to embed (see sign_raw()).

Returns

An asn1crypto.cms.SignerInfo object.

sign(data_digest: bytes, digest_algorithm: str, timestamp: Optional[datetime.datetime] = None, dry_run=False, revocation_info=None, use_pades=False, timestamper=None, cades_signed_attr_meta: Optional[pyhanko.sign.ades.api.CAdESSignedAttrSpec] = None, encap_content_info=None) → asn1crypto.cms.ContentInfo¶

Produce a detached CMS signature from a raw data digest.

Parameters

data_digest – Digest of the actual content being signed.
digest_algorithm – Digest algorithm to use. This should be the same digest method as the one used to hash the (external) content.
timestamp –
Signing time to embed into the signed attributes (will be ignored if use_pades is True).

Note

This timestamp value is to be interpreted as an unfounded assertion by the signer, which may or may not be good enough for your purposes.
dry_run –
If True, the actual signing step will be replaced with a placeholder.

In a PDF signing context, this is necessary to estimate the size of the signature container before computing the actual digest of the document.
revocation_info – Revocation information to embed; this should be the output of a call to Signer.format_revinfo() (ignored when use_pades is True).
use_pades – Respect PAdES requirements.
timestamper –
TimeStamper used to obtain a trusted timestamp token that can be embedded into the signature container.

Note

If dry_run is true, the timestamper’s dummy_response() method will be called to obtain a placeholder token. Note that with a standard HTTPTimeStamper, this might still hit the timestamping server (in order to produce a realistic size estimate), but the dummy response will be cached.
cades_signed_attr_meta –

New in version 0.5.0.

Specification for CAdES-specific signed attributes.
encap_content_info –
Data to encapsulate in the CMS object.

Danger

This parameter is internal API, and must not be used to produce PDF signatures.

Returns

An ContentInfo object.

sign_prescribed_attributes(digest_algorithm: str, signed_attrs: asn1crypto.cms.CMSAttributes, cms_version='v1', dry_run=False, timestamper=None, encap_content_info=None) → asn1crypto.cms.ContentInfo¶

Start the CMS signing process with the prescribed set of signed attributes.

Parameters

digest_algorithm – Digest algorithm to use. This should be the same digest method as the one used to hash the (external) content.
signed_attrs – CMS attributes to sign.
dry_run –
If True, the actual signing step will be replaced with a placeholder.

In a PDF signing context, this is necessary to estimate the size of the signature container before computing the actual digest of the document.
timestamper –
TimeStamper used to obtain a trusted timestamp token that can be embedded into the signature container.

Note

If dry_run is true, the timestamper’s dummy_response() method will be called to obtain a placeholder token. Note that with a standard HTTPTimeStamper, this might still hit the timestamping server (in order to produce a realistic size estimate), but the dummy response will be cached.
cms_version – CMS version to use.
encap_content_info –
Data to encapsulate in the CMS object.

Danger

This parameter is internal API, and must not be used to produce PDF signatures.

Returns

An ContentInfo object.

sign_general_data(input_data: Union[IO, bytes, asn1crypto.cms.ContentInfo, asn1crypto.cms.EncapsulatedContentInfo], digest_algorithm: str, detached=True, timestamp: Optional[datetime.datetime] = None, use_cades=False, timestamper=None, cades_signed_attr_meta: Optional[pyhanko.sign.ades.api.CAdESSignedAttrSpec] = None, chunk_size=4096, max_read=None) → asn1crypto.cms.ContentInfo¶

Produce a CMS signature for an arbitrary data stream (not necessarily PDF data).

New in version 0.7.0.

Parameters

input_data –
The input data to sign. This can be either a bytes object a file-type object, a cms.ContentInfo object or a cms.EncapsulatedContentInfo object.

Warning

asn1crypto mandates cms.ContentInfo for CMS v1 signatures. In practical terms, this means that you need to use cms.ContentInfo if the content type is data, and cms.EncapsulatedContentInfo otherwise.

Warning

We currently only support CMS v1 and v3 signatures. This is only a concern if you need attribute certificate support, in which case you can override the CMS version number yourself (this will not invalidate any signatures).
digest_algorithm – The name of the digest algorithm to use.
detached – If True, create a CMS detached signature (i.e. an object where the encapsulated content is not embedded in the signature object itself). This is the default. If False, the content to be signed will be embedded as encapsulated content.
timestamp –
Signing time to embed into the signed attributes (will be ignored if use_cades is True).

Note

This timestamp value is to be interpreted as an unfounded assertion by the signer, which may or may not be good enough for your purposes.
use_cades – Construct a CAdES-style CMS object.
timestamper –
PdfTimeStamper to use to create a signature timestamp

Note

If you want to create a content timestamp (as opposed to a signature timestamp), see CAdESSignedAttrSpec.
cades_signed_attr_meta – Specification for CAdES-specific signed attributes.
chunk_size – Chunk size to use when consuming input data.
max_read – Maximal number of bytes to read from the input stream.

Returns

A CMS ContentInfo object of type signedData.

class pyhanko.sign.signers.pdf_cms.SimpleSigner(signing_cert: asn1crypto.x509.Certificate, signing_key: asn1crypto.keys.PrivateKeyInfo, cert_registry: pyhanko.sign.general.CertificateStore, signature_mechanism: Optional[asn1crypto.algos.SignedDigestAlgorithm] = None, prefer_pss=False)¶

Bases: pyhanko.sign.signers.pdf_cms.Signer

Simple signer implementation where the key material is available in local memory.

signing_key: asn1crypto.keys.PrivateKeyInfo¶: Private key associated with the certificate in signing_cert.

sign_raw(data: bytes, digest_algorithm: str, dry_run=False) → bytes¶

Compute the raw cryptographic signature of the data provided, hashed using the digest algorithm provided.

Parameters

data – Data to sign.
digest_algorithm –
Digest algorithm to use.

Warning

If signature_mechanism also specifies a digest, they should match.
dry_run – Do not actually create a signature, but merely output placeholder bytes that would suffice to contain an actual signature.

Returns

Signature bytes.

classmethod load_pkcs12(pfx_file, ca_chain_files=None, passphrase=None, signature_mechanism=None, prefer_pss=False)¶

Load certificates and key material from a PCKS#12 archive (usually .pfx or .p12 files).

Parameters

pfx_file – Path to the PKCS#12 archive.
ca_chain_files – Path to (PEM/DER) files containing other relevant certificates not included in the PKCS#12 file.
passphrase – Passphrase to decrypt the PKCS#12 archive, if required.
signature_mechanism – Override the signature mechanism to use.
prefer_pss – Prefer PSS signature mechanism over RSA PKCS#1 v1.5 if there’s a choice.

Returns

A SimpleSigner object initialised with key material loaded from the PKCS#12 file provided.

classmethod load(key_file, cert_file, ca_chain_files=None, key_passphrase=None, other_certs=None, signature_mechanism=None, prefer_pss=False)¶

Load certificates and key material from PEM/DER files.

Parameters

key_file – File containing the signer’s private key.
cert_file – File containing the signer’s certificate.
ca_chain_files – File containing other relevant certificates.
key_passphrase – Passphrase to decrypt the private key (if required).
other_certs – Other relevant certificates, specified as a list of asn1crypto.x509.Certificate objects.
signature_mechanism – Override the signature mechanism to use.
prefer_pss – Prefer PSS signature mechanism over RSA PKCS#1 v1.5 if there’s a choice.

Returns

A SimpleSigner object initialised with key material loaded from the files provided.

class pyhanko.sign.signers.pdf_cms.ExternalSigner(signing_cert: asn1crypto.x509.Certificate, cert_registry: pyhanko.sign.general.CertificateStore, signature_value: bytes, signature_mechanism: Optional[asn1crypto.algos.SignedDigestAlgorithm] = None, prefer_pss=False)¶

Bases: pyhanko.sign.signers.pdf_cms.Signer

Class to help formatting CMS objects for use with remote signing. It embeds a fixed signature value into the CMS, set at initialisation.

Intended for use with Interrupted signing.

signing_cert: asn1crypto.x509.Certificate¶: The certificate that will be used to create the signature.

cert_registry: pyhanko.sign.general.CertificateStore¶: Collection of certificates associated with this signer. Note that this is simply a bookkeeping tool; in particular it doesn’t care about trust.

sign_raw(data: bytes, digest_algorithm: str, dry_run=False) → bytes¶: Return a fixed signature value.

class pyhanko.sign.signers.pdf_cms.PdfCMSSignedAttributes(signing_time: Optional[datetime.datetime] = None, adobe_revinfo_attr: Optional[asn1crypto.cms.CMSAttribute] = None, cades_signed_attrs: Optional[pyhanko.sign.ades.api.CAdESSignedAttrSpec] = None)¶

Bases: object

New in version 0.7.0.

Serialisable container class describing input for various signed attributes in a CMS object for a PDF signature.

signing_time: Optional[datetime.datetime] = None¶: Timestamp for the signingTime attribute. Will be ignored in a PAdES context.

adobe_revinfo_attr: Optional[asn1crypto.cms.CMSAttribute] = None¶: Adobe-style signed revocation info attribute.

cades_signed_attrs: Optional[pyhanko.sign.ades.api.CAdESSignedAttrSpec] = None¶: Optional settings for CAdES-style signed attributes.