Key management is the management of cryptographic keys in a cryptosystem. This includes dealing with the generation, exchange, storage, use, and replacement of keys. It includes cryptographic protocol design, key servers, user procedures, and other relevant protocols.
Key management concerns keys at the user level, either between users or systems. This is in contrast to key scheduling; key scheduling typically refers to the internal handling of key material within the operation of a cipher.
Successful key management is critical to the security of a cryptosystem. In practice it is arguably the most difficult aspect of cryptography because it involves system policy, user training, organizational and departmental interactions, and coordination between all of these elements.
Types of keys 
Cryptographic systems may use different types of keys, with some systems using more than one. These may include symmetric keys or asymmetric keys. In a symmetric key algorithm the keys involved are identical for both encrypting and decrypting a message. Keys must be chosen carefully, and distributed and stored securely. Asymmetric keys, in contrast, are two distinct keys that are mathematically linked. They are typically used in conjunction to communicate.
Key exchange 
Prior to any secured communication, users must setup the details of the cryptography. In some instances this may require exchanging identical keys (in the case of a symmetric key system). In others it may require possessing the other party's public key. While public keys can be openly exchanged (their corresponding private key is kept secret), symmetric keys must be exchanged over a secure communication channel. Formerly, exchange of such a key was extremely troublesome, and was greatly eased by access to secure channels such as a diplomatic bag. Clear text exchange of symmetric keys would enable any interceptor to immediately learn the key, and any encrypted data.
The advance of public key cryptography in the 1970s has made the exchange of keys less troublesome. Since the Diffie-Hellman key exchange protocol was published in 1975, it has become possible to exchange a key over an insecure communications channel, which has substantially reduced the risk of key disclosure during distribution. It is possible, using something akin to a book code, to include key indicators as clear text attached to an encrypted message. The encryption technique used by Richard Sorge's code clerk was of this type, referring to a page in a statistical manual, though it was in fact a code. The German Army Enigma symmetric encryption key was a mixed type early in its use; the key was a combination of secretly distributed key schedules and a user chosen session key component for each message.
In more modern systems, such as OpenPGP compatible systems, a session key for a symmetric key algorithm is distributed encrypted by an asymmetric key algorithm. This approach avoids even the necessity for using a key exchange protocol like Diffie-Hellman key exchange.
Another method of key exchange involves encapsulating one key within another. Typically a master key is generated and exchanged using some secure method. This method is usually cumbersome or expensive (breaking a master key into multiple parts and sending each with a trusted courier for example) and not suitable for use on a larger scale. Once the master key has been securely exchanged, it can then be used to securely exchange subsequent keys with ease. This technique is usually termed Key Wrap. A common technique uses Block ciphers and cryptographic hash functions.
A related method is to exchange a master key (sometimes termed a root key) and derive subsidiary keys as needed from that key and some other data (often referred to as diversification data). The most common use for this method is probably in SmartCard based cryptosystems, such as those found in banking cards. The bank or credit network embeds their secret key into the card's secure key storage during card production at a secured production facility. Then at the Point of sale the card and card reader are both able to derive a common set of session keys based on the shared secret key and card-specific data (such as the card serial number). This method can also be used when keys must be related to each other (i.e., departmental keys are tied to divisional keys, and individual keys tied to departmental keys). However, tying keys to each other in this way increases the damage which may result from a security breach as attackers will learn something about more than one key. This reduces entropy, with regard to an attacker, for each key involved.
Key storage 
However distributed, keys must be stored securely to maintain communications security. There are various techniques in use to do so. Likely the most common is that an encryption application manages keys for the user and depends on an access password to control use of the key.
Key use 
The major issue is length of key use, and therefore frequency of replacement. Because it increases any attackers required effort, keys should be frequently changed. This also limits loss of information, as the number of stored encrypted messages which will become readable when a key is found will decrease as the frequency of key change increases. Historically, symmetric keys have been used for long periods in situations in which key exchange was very difficult or only possible intermittently. Ideally, the symmetric key should change with each message or interaction, so that only that message will become readable if the key is learned (e.g., stolen, cryptanalyzed, or social engineered).
Public Key Infrastructure (PKI) 
A public key infrastructure is a type of key management system that uses hierarchical digital certificates to provide authentication, and public keys to provide encryption. PKIs are used in World Wide Web traffic, commonly in the form of SSL and TLS.
Enterprise Key and Certificate Management (EKCM) 
The starting point in any certificate and private key management strategy is to create a comprehensive inventory of all certificates, their locations and responsible parties. This is not a trivial matter because certificates from a variety of sources are deployed in a variety of locations by different individuals and teams - it's simply not possible to rely on a list from a single certificate authority. Certificates that are not renewed and replaced before they expire can cause serious downtime and outages. Some other considerations:
- Regulations and requirements, like PCI-DSS, demand stringent security and management of cryptographic keys and auditors are increasingly reviewing the management controls and processes in use.
- Private keys used with certificates must be kept secure or unauthorised individuals can intercept confidential communications or gain unauthorised access to critical systems. Failure to ensure proper segregation of duties means that admins who generate the encryption keys can use them to access sensitive, regulated data.
- If a certificate authority is compromised or an encryption algorithm is broken, organizations must be prepared to replace all of their certificates and keys in a matter of hours.
Multicast Group Key Management 
Group Key Management means managing the keys in a group communication. Most of the group communications use multicast communication because if the message is sent once by the sender, it will be received by all the users. Main problem in multicast group communication is its security. In order to improve the security, various keys are given to the users. Using the keys the users can encrypt their messages and send secretly.
Challenges of Key Management 
Several challenges IT organizations face when trying to control and manage their encryption keys are:
- Complex Management: Managing a plethora of encryption keys in the millions.
- Security Issues: Vulnerability of keys from outside hackers/malicious insiders.
- Data Availability: Ensuring data accessibility for authorized users.
- Scalability: Supporting multiple databases, applications and standards.
- Governance: Defining policy driven, access, control and protection for data.
Types of Key Management Systems 
There are two types of key management systems
- Integrated Key Management System
- Third-Party Key Management System
Key Management Commercial Systems 
The following list of key management systems exist commercially
- Bell ID Key Manager 
- Cryptsoft KMIP C and Java Servers
- Venafi Encryption Director
- HP Enterprise Secure Key Manager 
- IBM Tivoli Key Lifecycle Manager 
- IBM Enterprise Key Management Foundation 
- IBM Distributed Key Management System (DKMS) 
- Oracle Key Manager 
- QuintessenceLabs Key Manager 
- RSA Data Protection Manager 
- Safenet Enterprise Key Management 
- Thales Key Management 
- Townsend Security Alliance Key Manager 
- Gazzang zTrustee
- Unitech Power Technology Co. http://www.ut-power.com/English/Solution/Index/id/4.html
- Porticor Virtual Private Data 
See also 
- Key (cryptography)
- Key exchange
- NSA's Electronic Key Management System (EKMS)
- Public key infrastructure
- Assorted list of cryptographic key types
- Physical key management
- Key Ceremony
- Key encapsulation
- Key Wrap
- Key derivation function
- Pseudorandom function family
- Symmetric key algorithm
- Recommendation for Key Management — Part 1: general, NIST Special Publication 800-57
- NIST Cryptographic Toolkit
- The IEEE Security in Storage Working Group (SISWG) that is creating the P1619.3 standard for Key Management
- American National Standards Institute - ANSI X9.24, Retail Financial Services Symmetric Key Management
- The OASIS Key Management Interoperability Protocol (KMIP) Technical Committee
- The OASIS Enterprise Key Management Infrastructure (EKMI)Technical Committee
- "Types of Key Management"
- "Key Management with a Powerful Keystore"