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CRYPT_E_UNKNOWN_ALGO
The encoded CMS/PKCS#7 message names a cryptographic algorithm that the current CryptoAPI path does not recognize or support.
What to check for CRYPT_E_UNKNOWN_ALGO
- Inspect the message algorithm identifier and object identifier (OID) before changing any system cryptography policy.
- Confirm that the sender and recipient agree on the CMS message profile and supported algorithms.
- Do not re-enable legacy algorithms merely to suppress the error; choose a supported algorithm or update the producing system.
Microsoft: CryptMsgOpenToDecode
Microsoft: CryptVerifyMessageSignature
Diagnostic interpretation of CRYPT_E_UNKNOWN_ALGO
CRYPT_E_UNKNOWN_ALGO has the HRESULT value 0x80091002. AllStat records the condition as “Unknown cryptographic algorithm.”. For CRYPT_E_UNKNOWN_ALGO, in practice, interpret that wording at the boundary owned by cryptography, certificate, trust, or key-provider processing, rather than treating the value as a generic Windows message.
Evidence to capture for CRYPT_E_UNKNOWN_ALGO
- Record the exact COM method or Windows API, its input object, the calling thread, and the full 0x80091002 value before a wrapper converts it to an exception or Boolean result.
- Capture any IErrorInfo text, activity identifier, event-log entry, and subsystem trace that mentions CRYPT_E_UNKNOWN_ALGO or the crypt / unknown / algo operation.
- Preserve the first failure in the call chain; a later HRESULT can describe cleanup rather than the original crypt / unknown / algo condition.
Retry and recovery for CRYPT_E_UNKNOWN_ALGO
Retry CRYPT_E_UNKNOWN_ALGO only when the owning API documents a transient state or after the condition described as “Unknown cryptographic algorithm.” has changed. For CRYPT_E_UNKNOWN_ALGO, configuration, policy, format, and authorization failures normally require correction first; an immediate loop can hide the original call site and add secondary errors.
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