.NET System.Security.Cryptography

Facts and the checks behind them

Nothing below is copied from documentation. The check content/libraries/verify/dotnet-crypto/run.sh ran .NET System.Security.Cryptography 10.0.13 on .NET 10.0.13 on Ubuntu 24.04.5 LTS in the container image mcr.microsoft.com/dotnet/sdk:10.0.402-noble on October 20, 2026; the page must match what it printed, and each fact lists those lines.

• ECDSA signature encoding

  raw

  SignData returns 64 bytes of IEEE P1363 r‖s by default; DSASignatureFormat.Rfc3279DerSequence produces DER.

  Recorded by the check

  fact ecdsa-signature-encoding = raw
  evidence ecdsa-signature-encoding: SignData default: 64 bytes; with Rfc3279DerSequence: parses as DER True

• ECDSA nonce

  random

  Random nonce: the RFC 6979 key signed the same message twice with different results.

  Recorded by the check

  fact ecdsa-nonce = random

• Low-S when signing

  either

  s is not normalized: high-S values appeared among 64 signatures.

  Recorded by the check

  fact ecdsa-low-s-sign = either

• High-S when verifying

  accepts-high-s

  A signature with s replaced by n − s verified.

  Recorded by the check

  fact ecdsa-low-s-verify = accepts-high-s

• What the signing call hashes

  hashes-message-or-digest

  SignData hashes; SignHash signs a digest you computed, and that signature verified against the message.

  Recorded by the check

  fact ecdsa-prehash = hashes-message-or-digest

• Malformed ECDSA signature

  returns-false

  A DER signature checked as P1363, a raw signature checked as DER and a 3-byte blob all return false.

  Recorded by the check

  fact ecdsa-malformed-signature = returns-false
  evidence ecdsa-malformed-signature: DER to the default verifier: false; raw to the DER verifier: false; 3 bytes: false

• ECDSA curves

  P-256P-384P-521secp256k1brainpoolP256r1brainpoolP384r1brainpoolP512r1

  P-256, P-384, P-521, secp256k1 and brainpoolP256r1/P384r1/P512r1 signed and verified on Linux.

  Recorded by the check

  fact ecdsa-curves = P-256, P-384, P-521, secp256k1, brainpoolP256r1, brainpoolP384r1, brainpoolP512r1

• EdDSA

  none

  There is no Ed25519 class in System.Security.Cryptography.

  Recorded by the check

  fact eddsa = none
  evidence eddsa: System.Security.Cryptography.Ed25519 type present: False

• Post-quantum algorithms

  none

  MLKem.IsSupported, MLDsa.IsSupported, SlhDsa.IsSupported and composite ML-DSA support were all false on this platform.

  Recorded by the check

  fact pqc = none
  evidence pqc: MLKem.IsSupported False, MLDsa.IsSupported False, SlhDsa.IsSupported False, CompositeMLDsa.IsSupported(MLDsa65WithECDsaP256) False

• Platform OpenSSL

  3.0.13

  On Linux the classes use the system OpenSSL, here 3.0.13 from Ubuntu 24.04, which predates ML-KEM and ML-DSA.

  Recorded by the check

  fact platform-openssl = 3.0.13
  evidence platform-openssl: OpenSSL 3.0.13 30 Jan 2024 (Library: OpenSSL 3.0.13 30 Jan 2024)

• Public key formats

  spki-pemspki-derraw-xy

  Public keys import from SPKI PEM (ImportFromPem), SPKI DER and the raw X and Y coordinates in ECParameters.

  Recorded by the check

  fact public-key-formats = spki-pem, spki-der, raw-xy
  evidence public-key-formats: ImportParameters takes Q.X and Q.Y separately; there is no SEC1 point or JWK import in the BCL

• Private key formats

  pkcs8-pempkcs8-derencrypted-pkcs8sec1-pemsec1-derraw-scalar

  Private keys import from PKCS#8 PEM and DER, encrypted PKCS#8, SEC1 PEM and DER, and the raw scalar in ECParameters.

  Recorded by the check

  fact private-key-formats = pkcs8-pem, pkcs8-der, encrypted-pkcs8, sec1-pem, sec1-der, raw-scalar

Usage

using System.Security.Cryptography;
using System.Text;

using var key = ECDsa.Create(ECCurve.NamedCurves.nistP256);
var message = Encoding.UTF8.GetBytes("order #1042 approved");

// .NET signs raw r||s (IEEE P1363) by default; OpenSSL, Java and Go expect DER.
var raw = key.SignData(message, HashAlgorithmName.SHA256);
var der = key.SignData(message, HashAlgorithmName.SHA256, DSASignatureFormat.Rfc3279DerSequence);

// Verifying a DER signature needs the same format argument, or VerifyData returns false.
var ok = key.VerifyData(message, der, HashAlgorithmName.SHA256, DSASignatureFormat.Rfc3279DerSequence);
var wrongFormat = key.VerifyData(message, der, HashAlgorithmName.SHA256);
Console.WriteLine($"raw: {raw.Length} bytes, DER verified: {ok}, DER as raw: {wrongFormat}");
Console.WriteLine(key.ExportSubjectPublicKeyInfoPem().Split('\n')[0]);