openpgp: Add crypto::backend that identifies the backend.

  - This returns a short, human-readable description of the
    cryptographic backend for use in version strings to improve bug
    reports.

  - Fixes #818.

5 files changed, 29 insertions, 0 deletions

diff --git a/openpgp/NEWS b/openpgp/NEWS
index c458e9bc..416e51f7 100644
--- a/openpgp/NEWS
+++ b/openpgp/NEWS
@@ -4,6 +4,7 @@
 
 * Changes in 1.9.0
 ** New functionality
+   - crypto::backend
    - packet::Any
    - Packet::version
    - SignatureBuilder::set_reference_time
diff --git a/openpgp/src/crypto/backend/cng.rs b/openpgp/src/crypto/backend/cng.rs
index f964756a..89f56e31 100644
--- a/openpgp/src/crypto/backend/cng.rs
+++ b/openpgp/src/crypto/backend/cng.rs
@@ -10,6 +10,12 @@ pub mod ecdh;
 pub mod hash;
 pub mod symmetric;
 
+/// Returns a short, human-readable description of the backend.
+pub fn backend() -> String {
+    // XXX: can we include features and the version?
+    "Windows CNG".to_string()
+}
+
 /// Fills the given buffer with random data.
 pub fn random(buf: &mut [u8]) {
     RandomNumberGenerator::system_preferred()
diff --git a/openpgp/src/crypto/backend/nettle.rs b/openpgp/src/crypto/backend/nettle.rs
index 79497a66..3de8a6a9 100644
--- a/openpgp/src/crypto/backend/nettle.rs
+++ b/openpgp/src/crypto/backend/nettle.rs
@@ -10,6 +10,13 @@ pub mod ecdh;
 pub mod hash;
 pub mod symmetric;
 
+/// Returns a short, human-readable description of the backend.
+pub fn backend() -> String {
+    // XXX: Once we depend on nettle-rs 7.1, add cv448 feature
+    // XXX: Once we depend on nettle-rs 7.2, add nettle::version
+    "Nettle".to_string()
+}
+
 /// Fills the given buffer with random data.
 pub fn random(buf: &mut [u8]) {
     Yarrow::default().random(buf);
diff --git a/openpgp/src/crypto/backend/rust.rs b/openpgp/src/crypto/backend/rust.rs
index 06b1da03..dc4773ed 100644
--- a/openpgp/src/crypto/backend/rust.rs
+++ b/openpgp/src/crypto/backend/rust.rs
@@ -9,6 +9,12 @@ pub mod ecdh;
 pub mod hash;
 pub mod symmetric;
 
+/// Returns a short, human-readable description of the backend.
+pub fn backend() -> String {
+    // XXX: can we include features and the version?
+    "RustCrypto".to_string()
+}
+
 /// Fills the given buffer with random data.
 pub fn random(buf: &mut [u8]) {
     use rand07::rngs::OsRng;
diff --git a/openpgp/src/crypto/mod.rs b/openpgp/src/crypto/mod.rs
index e3cfa197..6dc2002d 100644
--- a/openpgp/src/crypto/mod.rs
+++ b/openpgp/src/crypto/mod.rs
@@ -43,6 +43,15 @@ pub(crate) mod symmetric;
 #[cfg(test)]
 mod tests;
 
+/// Returns a short, human-readable description of the backend.
+///
+/// This starts with the name of the backend, possibly a version, and
+/// any optional features that are available.  This is meant for
+/// inclusion in version strings to improve bug reports.
+pub fn backend() -> String {
+    backend::backend()
+}
+
 /// Fills the given buffer with random data.
 ///
 /// Fills the given buffer with random data produced by a