doc: python bindings howto
* Replaced the single encryption methods with one main way (i.e. cut the low level stuff involving SEEK_SET instructions).
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Ben McGinnes
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@ -436,6 +436,7 @@
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section we will look at how to programmatically encrypt data,
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decrypt it, sign it and verify signatures.
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** Encryption
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption
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@ -446,85 +447,35 @@
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the second example the message will be encrypted to multiple
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recipients.
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*** Encrypting to one key
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption-single
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:END:
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The text is then encapsulated in a GPGME Data object as =plain= and
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the =cipher= object is created with another Data object. Then we
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create the Context as =c= and set it to use the ASCII armoured
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OpenPGP format. In later examples there will be alternative
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methods of setting the OpenPGP output to be ASCII armoured.
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Once the the Context is set the main issues with encrypting data
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is essentially reduced to key selection and the keyword arguments
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specified in the =gpg.Context().encrypt()= method.
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Next we prepare a keylist object in our Context and follow it with
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specifying the recipients as =r=. Note that the configuration in
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one's =gpg.conf= file is honoured, so if you have the options set
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to encrypt to one key or to a default key, that will be included
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with this operation.
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This is followed by a quick check to be sure that the recipient is
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actually selected and that the key is available. Assuming it is,
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the encryption can proceed, but if not a message will print stating
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the key was not found.
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The encryption operation is invoked within the Context with the
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=c.op_encrypt= function, loading the recipients (=r=), the message
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(=plain=) and the =cipher=. The =cipher.seek= uses =os.SEEK_SET=
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to set the data to the correct byte format for GPGME to use it.
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At this point we no longer need the plaintext material, so we
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delete both the =text= and the =plain= objects. Then we write the
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encrypted data out to a file, =secret_plans.txt.asc=.
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#+begin_src python
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import gpg
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import os
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rkey = "0x12345678DEADBEEF"
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text = """
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Some plain text to test with. Obtained from any input source Python can read.
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It makes no difference whether it is string or bytes, but the bindings always
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produce byte output data. Which is useful to know when writing out either the
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encrypted or decrypted results.
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"""
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plain = gpg.core.Data(text)
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cipher = gpg.core.Data()
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c = gpg.core.Context()
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c.set_armor(1)
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c.op_keylist_start(rkey, 0)
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r = c.op_keylist_next()
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if r == None:
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print("""The key for user "{0}" was not found""".format(rkey))
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else:
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try:
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c.op_encrypt([r], 1, plain, cipher)
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cipher.seek(0, os.SEEK_SET)
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with open("secret_plans.txt.asc", "wb") as afile:
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afile.write(cipher.read())
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except gpg.errors.GPGMEError as ex:
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print(ex.getstring())
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#+end_src
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*** Encrypting to one key using the second method
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption-monogamous
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:END:
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This example re-creates the first encryption example except it
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uses the same =encrypt= method used in the subsequent examples
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instead of the =op_encrypt= method. This means that, unlike the
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=op_encrypt= method, it /must/ use byte literal input data.
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Those keyword arguments are: =recipients=, a list of keys
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encrypted to (covered in greater detail in the following section);
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=sign=, whether or not to sign the plaintext data, see subsequent
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sections on signing and verifying signatures below (defaults to
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=True=); =sink=, to write results or partial results to a secure
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sink instead of returning it (defaults to =None=); =passphrase=,
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only used when utilising symmetric encryption (defaults to
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=None=); =always_trust=, used to override the trust model settings
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for recipient keys (defaults to =False=); =add_encrypt_to=,
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utilises any preconfigured =encrypt-to= or =default-key= settings
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in the user's =gpg.conf= file (defaults to =False=); =prepare=,
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prepare for encryption (defaults to =False=); =expect_sign=,
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prepare for signing (defaults to =False=); =compress=, compresses
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the plaintext prior to encryption (defaults to =True=).
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#+begin_src python
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import gpg
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rkey = "0x12345678DEADBEEF"
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a_key = "0x12345678DEADBEEF"
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text = b"""Some text to test with.
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Since the text in this case must be bytes, it is most likely that
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@ -534,56 +485,51 @@
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"""
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c = gpg.Context(armor=True)
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rpattern = list(c.keylist(pattern=rkey, secret=False))
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logrus = []
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for i in range(len(rpattern)):
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if rpattern[i].can_encrypt == 1:
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logrus.append(rpattern[i])
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cipher = c.encrypt(text, recipients=logrus, sign=False, always_trust=True)
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rkey = list(c.keylist(pattern=a_key, secret=False))
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ciphertext, result, sign_result = c.encrypt(text, recipients=rkey, sign=False)
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with open("secret_plans.txt.asc", "wb") as afile:
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afile.write(cipher[0])
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afile.write(ciphertext)
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#+end_src
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With one or two exceptions, this method will probably prove to be
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easier to implement than the first method and thus it is the
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recommended encryption method. Though it is even more likely to
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be used like this:
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Though this is even more likely to be used like this; with the
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plaintext input read from a file, the recipient keys used for
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encryption regardless of key trust status and the encrypted output
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also encrypted to any preconfigured keys set in the =gpg.conf=
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file:
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#+begin_src python
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import gpg
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rkey = "0x12345678DEADBEEF"
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a_key = "0x12345678DEADBEEF"
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afile = open("secret_plans.txt", "rb")
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with open("secret_plans.txt", "rb") as afile:
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text = afile.read()
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afile.close()
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c = gpg.Context(armor=True)
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rpattern = list(c.keylist(pattern=rkey, secret=False))
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logrus = []
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for i in range(len(rpattern)):
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if rpattern[i].can_encrypt == 1:
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logrus.append(rpattern[i])
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cipher = c.encrypt(text, recipients=logrus, sign=False, always_trust=True)
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rkey = list(c.keylist(pattern=a_key, secret=False))
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ciphertext, result, sign_result = c.encrypt(text, recipients=rkey,
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sign=True, always_trust=True,
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add_encrypt_to=True)
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with open("secret_plans.txt.asc", "wb") as afile:
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afile.write(cipher[0])
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afile.write(ciphertext)
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#+end_src
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If the =recipients= paramater is empty then the plaintext is
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encrypted symmetrically. If no =passphrase= is supplied as a
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parameter or via a callback registered with the =Context()= then
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an out-of-band prompt for the passphrase via pinentry will be
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invoked.
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*** Encrypting to multiple keys
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-encryption-multiple
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:END:
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Encrypting to multiple keys, in addition to a default key or a key
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configured to always encrypt to, is a little different and uses a
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slightly different call to the =op_encrypt= call demonstrated in the
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previous section.
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Encrypting to multiple keys essentially just expands upon the key
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selection process and the recipients from the previous examples.
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The following example encrypts a message (=text=) to everyone with
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an email address on the =gnupg.org= domain,[fn:3] but does /not/ encrypt
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@ -711,7 +657,8 @@
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:CUSTOM_ID: howto-basic-signing
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:END:
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The following sections demonstrate how to specify
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The following sections demonstrate how to specify keys to sign with.
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*** Signing key selection
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:PROPERTIES:
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@ -743,6 +690,7 @@
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bytes or None and not a list. A string with two fingerprints
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won't match any single key.
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*** Normal or default signing messages or files
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-signing-normal
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@ -798,6 +746,7 @@
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afile.write(signed[0])
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#+end_src
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*** Detached signing messages and files
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-signing-detached
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@ -840,6 +789,7 @@
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afile.write(signed[0])
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#+end_src
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*** Clearsigning messages or text
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:PROPERTIES:
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:CUSTOM_ID: howto-basic-signing-clear
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@ -1307,6 +1257,7 @@
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:CUSTOM_ID: cheats-and-hacks
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:END:
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** Group lines
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:PROPERTIES:
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:CUSTOM_ID: group-lines
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@ -1357,6 +1308,7 @@
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:CUSTOM_ID: copyright-and-license
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:END:
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** Copyright (C) The GnuPG Project, 2018
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:PROPERTIES:
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:CUSTOM_ID: copyright
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@ -1364,6 +1316,7 @@
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Copyright © The GnuPG Project, 2018.
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** License GPL compatible
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:PROPERTIES:
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:CUSTOM_ID: license
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