update to RSA 0.7.0 interfaces

[lumag]

This depends on RustCrypto/RSA#195 and needs updated md5 and ripemd crates to provide OIDs

Note: it might be simpler to just restore the rsa::Hash struct in the RSA crate.

[lumag]

@dignifiedquire @tarcieri I noticed a side effect of this conversion. The rpgp starts to accept large RSA keys. E.g. a diff from the test_parse_dump_6:

@@ -110188,7 +110189,43 @@
 }
  DEBUG pgp::packet::signature::types     > packet: 54696d204d6f726c6579203c74696d4064657277656e742e636f2e756b3e
  DEBUG pgp::packet::signature::types     > prefix: b40000001e
- WARN  key_test                          > verification failed: public key 6ea0fbcd0c9c1545: RSAError(PublicExponentTooLarge)
+ DEBUG pgp::packet::signature::types     > verifying key (revocation): Signature {
+    packet_version: Old,
+    config: SignatureConfig {
+        version: V4,
+        typ: KeyRevocation,
+        pub_alg: RSA,
+        hash_alg: SHA1,
+        created: None,
+        issuer: None,
+        unhashed_subpackets: [
+            Issuer(
+                KeyId(6ea0fbcd0c9c1545),
+            ),
+        ],
+        hashed_subpackets: [
+            SignatureCreationTime(
+                2016-08-16T05:10:41Z,
+            ),
+            RevocationReason(
+                KeyCompromised,
+                "This key was generated as part of the Evil32 project.\nIt is not owned by the user described in the UID.\nSee https://evil32.com/revoked for more details.",
+            ),
+        ],
+    },
+    signed_hash_value: "6994",
+    signature: ["9874eb7c4e439db3c84c12777c16da7fbc2bc63cc884dbc54e545c787be91dcf022fb7c968c86f7c34b02fe11ccf6ce69b72f0cde8cfabf465e74bf477ecc01313cc6a155faade5ea2edd64c35011430e10553cae9c32c423c7fa316611d8120a9c87664e9b9ac01eda731e400cb8eda343d34ab3bcdab7a220f522c5968aa90"],
+} - PublicKey {
+    packet_version: Old,
+    version: V4,
+    algorithm: RSA,
+    created_at: 2014-07-21T20:49:33Z,
+    expiration: None,
+    public_params: PublicParams::RSA {
+        n: Mpi(aeabf22ebf5c2a537a70711fdba3bcb3ab8be63c7caa9a17a3d03b0b6b9673bb9ba2a95e031751bafffe69e26638f9be08a6229005e92b23a263c276893a263224576d9a03ef1934c58c256b5617728b2b28e5d6ca555900fb7c081317f18dc391debb4c08b4fd76db051b66fcba120ba0bb24c4b95d199f1c3be8c49b178931),
+        e: Mpi(9058273b),
+    },
+}
  DEBUG pgp::composed::signed_key::public > primary key: KeyId(05a0a15688995548)
  DEBUG pgp::composed::signed_key::public >   signatures
  DEBUG pgp::packet::many                 > got packet: Ok(

If this is undesired, we'd have to fix the crate.

[lumag]

Hmm. Actually no. This is caused by the RSA crate changing max public exponent.

[tarcieri]

it might be simpler to just restore the rsa::Hash struct in the RSA crate.

Looking at this PR it seems like the HashAlgorithm enum in the rpgp crate provides effectively the same functionality as what Hash used to provide (i.e. runtime selection of hash function)

[dignifiedquire]

This solution looks good to me, thanks @lumag, happy to move forward with the changes on the rsa side based on this

[lumag]

Updated the dependency to point to the released 0.7.0 RSA crate.