我认为那个 DefaultSignatureAlgorithmIdentifierFinder 是bcmail API的一部分。它返回此API识别的算法标识符。 （查看加密消息语法）另一方面，有弹性的种姓提供者提供更多算法。您可以检查 DefaultSignatureAlgorithmIdentifierFinder 的来源，其中识别的算法是硬编码的：

I think that DefaultSignatureAlgorithmIdentifierFinder is part of the bcmail API. It returns algorithm identifiers recognized by this API. (Check Cryptographic Message Syntax) On the other hand the bouncy caste provider provides more algorithms. You may check the source of DefaultSignatureAlgorithmIdentifierFinder where the recognized algorithms are hardcoded:

algorithms.put("MD2WITHRSAENCRYPTION", PKCSObjectIdentifiers.md2WithRSAEncryption);
algorithms.put("MD2WITHRSA", PKCSObjectIdentifiers.md2WithRSAEncryption);
algorithms.put("MD5WITHRSAENCRYPTION", PKCSObjectIdentifiers.md5WithRSAEncryption);
algorithms.put("MD5WITHRSA", PKCSObjectIdentifiers.md5WithRSAEncryption);
algorithms.put("SHA1WITHRSAENCRYPTION", PKCSObjectIdentifiers.sha1WithRSAEncryption);
algorithms.put("SHA1WITHRSA", PKCSObjectIdentifiers.sha1WithRSAEncryption);
algorithms.put("SHA224WITHRSAENCRYPTION", PKCSObjectIdentifiers.sha224WithRSAEncryption);
algorithms.put("SHA224WITHRSA", PKCSObjectIdentifiers.sha224WithRSAEncryption);
algorithms.put("SHA256WITHRSAENCRYPTION", PKCSObjectIdentifiers.sha256WithRSAEncryption);
algorithms.put("SHA256WITHRSA", PKCSObjectIdentifiers.sha256WithRSAEncryption);
algorithms.put("SHA384WITHRSAENCRYPTION", PKCSObjectIdentifiers.sha384WithRSAEncryption);
algorithms.put("SHA384WITHRSA", PKCSObjectIdentifiers.sha384WithRSAEncryption);
algorithms.put("SHA512WITHRSAENCRYPTION", PKCSObjectIdentifiers.sha512WithRSAEncryption);
algorithms.put("SHA512WITHRSA", PKCSObjectIdentifiers.sha512WithRSAEncryption);
algorithms.put("SHA1WITHRSAANDMGF1", PKCSObjectIdentifiers.id_RSASSA_PSS);
algorithms.put("SHA224WITHRSAANDMGF1", PKCSObjectIdentifiers.id_RSASSA_PSS);
algorithms.put("SHA256WITHRSAANDMGF1", PKCSObjectIdentifiers.id_RSASSA_PSS);
algorithms.put("SHA384WITHRSAANDMGF1", PKCSObjectIdentifiers.id_RSASSA_PSS);
algorithms.put("SHA512WITHRSAANDMGF1", PKCSObjectIdentifiers.id_RSASSA_PSS);
algorithms.put("RIPEMD160WITHRSAENCRYPTION", TeleTrusTObjectIdentifiers.rsaSignatureWithripemd160);
algorithms.put("RIPEMD160WITHRSA", TeleTrusTObjectIdentifiers.rsaSignatureWithripemd160);
algorithms.put("RIPEMD128WITHRSAENCRYPTION", TeleTrusTObjectIdentifiers.rsaSignatureWithripemd128);
algorithms.put("RIPEMD128WITHRSA", TeleTrusTObjectIdentifiers.rsaSignatureWithripemd128);
algorithms.put("RIPEMD256WITHRSAENCRYPTION", TeleTrusTObjectIdentifiers.rsaSignatureWithripemd256);
algorithms.put("RIPEMD256WITHRSA", TeleTrusTObjectIdentifiers.rsaSignatureWithripemd256);
algorithms.put("SHA1WITHDSA", X9ObjectIdentifiers.id_dsa_with_sha1);
algorithms.put("DSAWITHSHA1", X9ObjectIdentifiers.id_dsa_with_sha1);
algorithms.put("SHA224WITHDSA", NISTObjectIdentifiers.dsa_with_sha224);
algorithms.put("SHA256WITHDSA", NISTObjectIdentifiers.dsa_with_sha256);
algorithms.put("SHA384WITHDSA", NISTObjectIdentifiers.dsa_with_sha384);
algorithms.put("SHA512WITHDSA", NISTObjectIdentifiers.dsa_with_sha512);
algorithms.put("SHA1WITHECDSA", X9ObjectIdentifiers.ecdsa_with_SHA1);
algorithms.put("ECDSAWITHSHA1", X9ObjectIdentifiers.ecdsa_with_SHA1);
algorithms.put("SHA224WITHECDSA", X9ObjectIdentifiers.ecdsa_with_SHA224);
algorithms.put("SHA256WITHECDSA", X9ObjectIdentifiers.ecdsa_with_SHA256);
algorithms.put("SHA384WITHECDSA", X9ObjectIdentifiers.ecdsa_with_SHA384);
algorithms.put("SHA512WITHECDSA", X9ObjectIdentifiers.ecdsa_with_SHA512);
algorithms.put("GOST3411WITHGOST3410", CryptoProObjectIdentifiers.gostR3411_94_with_gostR3410_94);
algorithms.put("GOST3411WITHGOST3410-94", CryptoProObjectIdentifiers.gostR3411_94_with_gostR3410_94);
algorithms.put("GOST3411WITHECGOST3410", CryptoProObjectIdentifiers.gostR3411_94_with_gostR3410_2001);
algorithms.put("GOST3411WITHECGOST3410-2001", CryptoProObjectIdentifiers.gostR3411_94_with_gostR3410_2001);
algorithms.put("GOST3411WITHGOST3410-2001", CryptoProObjectIdentifiers.gostR3411_94_with_gostR3410_2001);

干杯！