From b338286947bf385e38bd227b6279210a386955c8 Mon Sep 17 00:00:00 2001 From: Paul Schaub Date: Tue, 19 Dec 2023 17:25:12 +0100 Subject: [PATCH 1/4] Clarify the reason for OPS sigs more and tweak the text structure --- book/source/signing_data.md | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/book/source/signing_data.md b/book/source/signing_data.md index 3fe97eb..24e2c75 100644 --- a/book/source/signing_data.md +++ b/book/source/signing_data.md @@ -41,7 +41,7 @@ Note that {term}`data signatures` are distinct from [](/signing_ ## Detached signatures -A {term}`detached signature` is produced by calculating an {term}`OpenPGP signature` over the data intended for signing. The original data remains unchanged, and the {term}`OpenPGP signature` is stored as a standalone file. A {term}`detached signature` file can be distributed alongside or independent of the original data. The {term}`authenticity` and integrity of the original data file can be {term}`verified` by using the {term}`detached signature` file. +A {term}`detached signature` is produced by calculating an {term}`OpenPGP signature` over the data intended for signing. The original data remains unchanged, and the {term}`OpenPGP signature` is stored separately, e.g. as a standalone file. A {term}`detached signature` file can be distributed alongside or independent of the original data. The {term}`authenticity` and integrity of the original data file can be {term}`verified` by using the {term}`detached signature` file. This {term}`signature` format is especially useful for signing software releases and other files where it is imperative that the content remains unaltered during the signing process. @@ -54,7 +54,7 @@ This method is commonly used for signing or encrypting emails. Most email softwa OpenPGP defines two variant forms of inline-signed messages: -1. **{term}`One-pass signed messages`** This is the commonly used format for inline-signed messages. A signer can produce this format in one pass. +1. **{term}`One-pass signed messages`** This is the commonly used format for inline-signed messages. A signer can produce and a verifier verify this format in one pass. 2. **{term}`Prefixed signed messages`** This format predates[^inline-signature-formats] {term}`one-pass signed messages` and is conceptually slightly simpler. However, it has no strong benefits and is now rarely used. [^inline-signature-formats]: One-pass signing was first specified in RFC 2440. The format was not supported in PGP 2.6.x. @@ -68,7 +68,7 @@ This is the commonly used format for inline signed messages. A {term}`one-pass signed` {term}`OpenPGP message` consists of three segments: -1. [**One-pass signature packets**](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#one-pass-sig): These one or more {term}`packets` precede the signed data and enable {term}`signature` computation in one pass. +1. [**One-pass signature packets**](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#one-pass-sig): These one or more {term}`packets` precede the signed data and enable {term}`signature` computation (both creation and verification) in a single pass. 2. [**Literal data packet**](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#lit): This contains the original data (e.g., the body of a message), without additional interpretation or conversion. @@ -77,14 +77,20 @@ A {term}`one-pass signed` {term}`OpenPGP message` consi ```{note} Despite its name, a {term}`one-pass signature packet` is not a type of {term}`signature packet`. -Instead, it's a type of auxiliary packet that can be used in conjunction with {term}`signature packets`. Its use allows storing the {term}`signature packets` after the message body. +Instead, it's a type of auxiliary packet that can be used in conjunction with {term}`signature packets`. Its use allows storing the {term}`signature packets` after the message body. + +The position of the signature packet within the OpenPGP message is important for efficient data processing. The plaintext data might be large in size, and memory might be constrained. +The producer of a signed OpenPGP message wants to streamline the signature calculation process in such a way that allows to emit the data to be signed while calculating the signature. The signature itself is therefore appended to the data. +The verifier on the other hand needs to know the hash algorithm used to calculate the signature before starting the verification process. As a consequence, either the producer would need to pass the plaintext data twice, once to calculate the signature and a second time to emit the signed data (the result is a prefixed-signed message), or the verifier needs to process (and cache) the whole OpenPGP message to reach the signature packets at the end in order to determine the hash algorithm, to then re-process the whole message, verifying the signature. + +The one-pass signature solves this issue, by allowing both the creation and verification of a signed message in a single pass. ``` #### Creation -To produce an {term}`inline signature`, the {term}`signer` processes the entirety of the data by reading from an input file and writing into an output {term}`OpenPGP message` file. As the data is processed, the {term}`signer` simultaneously calculates a {term}`cryptographic signature`. This procedure results in the appending of a {term}`data signature packet` to the output {term}`OpenPGP message` file, where it can be efficiently stored. +To produce an {term}`inline signature`, the {term}`signer` decides on a hash algorithm and emits a {term}`one-pass signature packet` into the destination {term}`OpenPGP message`. This contains essential information such as the {term}`fingerprint` of the {term}`signing key` and the {term}`hash` algorithm used for computing the {term}`signature`'s {term}`hash digest`. The signer then processes the entirety of the plaintext data, emitting it as a {term}`literal data` into the message as well. Once the data is processed, the {term}`signer` calculates a {term}`cryptographic signature` using the calculated hash value. Lastly, the result is emitted as a {term}`data signature packet` to the output message, and the whole packet sequence can be efficiently stored or transmitted. -For efficient {term}`verification`, an application must understand how to handle the {term}`literal data` prior to its reading. This requirement is addressed by the {term}`one-pass signature packets` located at the beginning of {term}`inline-signed` messages. These {term}`packets` include essential information such as the {term}`fingerprint` of the {term}`signing key` and the {term}`hash` algorithm used for computing the {term}`signature`'s {term}`hash digest`. This setup enables the verifier to process the data correctly and efficiently. +For efficient {term}`verification`, an application must understand how to handle the {term}`literal data` prior to reading from it. This requirement is addressed by the {term}`one-pass signature packets` located at the beginning of {term}`inline-signed` messages. This setup enables the verifier to process the data correctly and efficiently in only a single pass. Strictly speaking, knowing just the hash algorithm would be sufficient to begin the verification process. However, having efficient access to the signer's fingerprint or key ID upfront allows OpenPGP software to fetch the signer's certificate(s) before processing the entirety of the - potentially large - signed data. This may, for example, involve downloading the certificate from a keyserver. In case fetching the signer's certificate(s) fails, or requires additional input from the user, it is better to signal the user about this before processing the data. @@ -103,7 +109,7 @@ Important to note, the {term}`signer`'s {term}`public key`, (prefixed-signature)= ### Prefixed signed message -A {term}`prefixed signed message` consists of {term}`signature packet(s)` followed by the message. This inline signature format serves the same function as a {term}`one-pass signed message`. For the verifier, the two formats are equally convenient. However, on the signer's side, it takes more computational work to generate a {term}`prefixed signed message`. +A {term}`prefixed signed message` consists of {term}`signature packet(s)` followed by the message. For the verifier, processing one-pass-signed and prefixed-signed messages are equally convenient. However, on the signer's side, it takes more resources to generate a {term}`prefixed signed message`. #### Structure From 23d97d691266e0447809584292379581cedfbc3d Mon Sep 17 00:00:00 2001 From: Paul Schaub Date: Tue, 19 Dec 2023 18:34:22 +0100 Subject: [PATCH 2/4] Incorporate diagram of OPS-signed message --- book/assets/drawio/ops-signed-message.drawio | 74 ++++++++++++++++++++ book/assets/drawio/ops-signed-message.svg | 3 + book/source/signing_data.md | 7 ++ 3 files changed, 84 insertions(+) create mode 100644 book/assets/drawio/ops-signed-message.drawio create mode 100644 book/assets/drawio/ops-signed-message.svg diff --git a/book/assets/drawio/ops-signed-message.drawio b/book/assets/drawio/ops-signed-message.drawio new file mode 100644 index 0000000..bedff83 --- /dev/null +++ b/book/assets/drawio/ops-signed-message.drawio @@ -0,0 +1,74 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/book/assets/drawio/ops-signed-message.svg b/book/assets/drawio/ops-signed-message.svg new file mode 100644 index 0000000..1079fa3 --- /dev/null +++ b/book/assets/drawio/ops-signed-message.svg @@ -0,0 +1,3 @@ + + +
One-Pass-Signature
Hash: SHA512
Fingerprint: 0xB0B0
One-Pass-Signature...
Literal Data
"Hello World!"
Literal Data...
Signature
Hash: SHA512
Issuer: B0B0
Signature...
One-Pass-Signature
Hash: SHA384
Fingerprint: 0xB0B1
One-Pass-Signature...
Signature
Hash: SHA512
Issuer: B0B1
Signature...
"Hello World!" is hashed
"Hello World!" is hashed
SHA512 Hash
SHA512 Hash
SHA384 Hash
SHA384 HashText is not SVG - cannot display \ No newline at end of file diff --git a/book/source/signing_data.md b/book/source/signing_data.md index 24e2c75..43cf0ed 100644 --- a/book/source/signing_data.md +++ b/book/source/signing_data.md @@ -74,6 +74,13 @@ A {term}`one-pass signed` {term}`OpenPGP message` consi 3. **{term}`Data signature packets`**: These contain the {term}`cryptographic signature` corresponding to the original data. +```{figure} plain_svg/ops-signed-message.svg +:name: fig-ops-signed-message +:alt: Depicts the structure of a one-pass-signed message. + +The structure of a one-pass signed message. +``` + ```{note} Despite its name, a {term}`one-pass signature packet` is not a type of {term}`signature packet`. From 70b6bd2f439dc1bde82bcaf495df707676f562b3 Mon Sep 17 00:00:00 2001 From: Paul Schaub Date: Tue, 19 Dec 2023 18:53:53 +0100 Subject: [PATCH 3/4] Fix diagrams --- book/assets/drawio/ops-signed-message.drawio | 38 ++++++++++---------- book/assets/drawio/ops-signed-message.svg | 2 +- 2 files changed, 20 insertions(+), 20 deletions(-) diff --git a/book/assets/drawio/ops-signed-message.drawio b/book/assets/drawio/ops-signed-message.drawio index bedff83..deaec9a 100644 --- a/book/assets/drawio/ops-signed-message.drawio +++ b/book/assets/drawio/ops-signed-message.drawio @@ -1,30 +1,30 @@ - + - + - + - + - + - + - + - + - + @@ -32,40 +32,40 @@ - + - + - + - + - + - + - + - + - + - + diff --git a/book/assets/drawio/ops-signed-message.svg b/book/assets/drawio/ops-signed-message.svg index 1079fa3..da6b370 100644 --- a/book/assets/drawio/ops-signed-message.svg +++ b/book/assets/drawio/ops-signed-message.svg @@ -1,3 +1,3 @@ -
One-Pass-Signature
Hash: SHA512
Fingerprint: 0xB0B0
One-Pass-Signature...
Literal Data
"Hello World!"
Literal Data...
Signature
Hash: SHA512
Issuer: B0B0
Signature...
One-Pass-Signature
Hash: SHA384
Fingerprint: 0xB0B1
One-Pass-Signature...
Signature
Hash: SHA512
Issuer: B0B1
Signature...
"Hello World!" is hashed
"Hello World!" is hashed
SHA512 Hash
SHA512 Hash
SHA384 Hash
SHA384 HashText is not SVG - cannot display \ No newline at end of file +
One-Pass-Signature
Hash: SHA512
Fingerprint: 0xB0B0
One-Pass-Signature...
Literal Data
"Hello World!"
Literal Data...
Signature
Hash: SHA512
Issuer: B0B0
Signature...
One-Pass-Signature
Hash: SHA384
Fingerprint: 0xB0B1
One-Pass-Signature...
Signature
Hash: SHA384
Issuer: B0B1
Signature...
"Hello World!" is hashed
"Hello World!" is hashed
SHA512 Hash
SHA512 Hash
SHA384 Hash
SHA384 HashText is not SVG - cannot display \ No newline at end of file From edc2c8322ddbb4b8000145e12f3f260c52c715b2 Mon Sep 17 00:00:00 2001 From: Paul Schaub Date: Tue, 19 Dec 2023 18:54:05 +0100 Subject: [PATCH 4/4] Add diagram for prefixed-signed message --- .../drawio/prefixed-signed-message.drawio | 63 +++++++++++++++++++ .../assets/drawio/prefixed-signed-message.svg | 3 + book/source/signing_data.md | 9 ++- 3 files changed, 74 insertions(+), 1 deletion(-) create mode 100644 book/assets/drawio/prefixed-signed-message.drawio create mode 100644 book/assets/drawio/prefixed-signed-message.svg diff --git a/book/assets/drawio/prefixed-signed-message.drawio b/book/assets/drawio/prefixed-signed-message.drawio new file mode 100644 index 0000000..aea991e --- /dev/null +++ b/book/assets/drawio/prefixed-signed-message.drawio @@ -0,0 +1,63 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/book/assets/drawio/prefixed-signed-message.svg b/book/assets/drawio/prefixed-signed-message.svg new file mode 100644 index 0000000..1ee49bf --- /dev/null +++ b/book/assets/drawio/prefixed-signed-message.svg @@ -0,0 +1,3 @@ + + +
Literal Data
"Hello World!"
Literal Data...
Signature
Hash: SHA384
Issuer: B0B0
Signature...
Signature
Hash: SHA512
Issuer: B0B1
Signature...
"Hello World!" is hashed
"Hello World!" is hashed
SHA512 Hash
SHA512 Hash
SHA384 Hash
SHA384 HashText is not SVG - cannot display \ No newline at end of file diff --git a/book/source/signing_data.md b/book/source/signing_data.md index 43cf0ed..4921348 100644 --- a/book/source/signing_data.md +++ b/book/source/signing_data.md @@ -76,7 +76,7 @@ A {term}`one-pass signed` {term}`OpenPGP message` consi ```{figure} plain_svg/ops-signed-message.svg :name: fig-ops-signed-message -:alt: Depicts the structure of a one-pass-signed message. +:alt: Depicts the structure of a one-pass-signed message. Two one-pass-signatures lead the literal data packet, followed by two signature packets. Arrows show, how the hash-algorithm field of the one-pass-signatures is inspected in order to initiate the hashing procedure. The structure of a one-pass signed message. ``` @@ -126,6 +126,13 @@ In this format, the signature packets are stored ahead of the message itself: 2. [**Literal data packet**](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#lit): This contains the original data (e.g., the body of a message), without additional interpretation or conversion. +```{figure} plain_svg/prefixed-signed-message.svg +:name: fig-prefixed-signed-message +:alt: Depicts the structure of a prefixed-signed message. As an example, two signature packets lead a literal data packet. Arrows show, how the signatures hash algorithm field is inspected to start the hashing procedure. + +Structure of a prefixed-signed message. +``` + Compared to a {term}`one-pass signed message`, there are no {term}`one-pass signature packets` in this format, and the (otherwise equivalent) {term}`signature packet(s)` are stored ahead of the signed data. For verification, this is equally convenient as the one-pass signed message form.